The essence of Maggie Smith’s greatness as an actor was in her timing. She could be extravagantly physically expressive, getting bold effects with the angular tilt of her head and particularly with the gesticulations of her arms and her snake-charming wrists, which seemed to have a life of their own. But what made her so lethal was her timing, the way she could emphasize a syllable of a word or take a pause to really make a barb land. Fellow actors were frightened of her, and she was known in acting circles as “the Acid Queen.”

As a child, Smith kept to herself, but she could be tart and sarcastic from the sidelines, and she had a quiet war going on with her mother, a penny-pinching stickler for propriety who was very discouraging when Smith said she wanted to go on the stage. Because of this upbringing, Smith intimately knew the kind of lower-class British striving for gentility that made her mother such a tyrant, and she used this knowledge in both comedy and drama.

Smith impressed a teacher at school with her delivery of a speech from A Midsummer Night’s Dream: “She sent it up!” the teacher said, “a child of 14…she had, even then, marvelous comedy timing, and she never made a mistake.” Yet Smith was sometimes passed over for lead roles, and she held a grudge about this until the end of her life. Once while being interviewed about her early years, Smith remembered a girl who always got the lead over her in plays: “Veronica East,” Smith said, in that constricted voice of hers that sounded covered in snow and layers of ice. And then she took a killing pause before saying, “You see her name…everywhere.” Smith had at this point won two Oscars and was widely viewed as an ornament in her profession, set at the very top of the tree, but this did not mean that she had ever or could ever forgive Veronica East.

Smith began getting attention with work in comic revues, and she took a lot from working with the camp comic comedian Kenneth Williams; she thrived among gay men like Williams and enjoyed a good gossip, what she called “laying people out to filth.” She met her first husband, the actor Robert Stephens, while they were acting together on stage. “She was very raunchy,” Stephens said, and this impressed him for a time, but Stephens was a womanizer who couldn’t have been more indiscreet with his liaisons, and this only added to Smith’s simmering fury.

In the 1960s, Smith joined the National Theatre and was a leading lady for the head of that company, Laurence Olivier, thought then by many to be the greatest living actor, and definitely one of the most competitive. When Smith received a review saying that she had acted him off the stage in Ibsen’s The Master Builder, the scheming Olivier tried to throw off her acclaimed performance by telling her that she was delivering her lines too slowly. Realizing what he was doing, Smith responded by delivering her lines so rapidly at their next performance that she managed to throw Olivier himself totally off his game. She was that formidable and unafraid and tough from the start.

Smith began acting in movies, making a soulful impression in “The V.I.P.s” (1963) and “Young Cassidy” (1965), where she is movingly in love with Rod Taylor, and she scored in the small part of the devious Philpot in “The Pumpkin Eater” (1964). On stage, she made a particular success at the National in Franco Zeffirelli’s Italianate production of Much Ado About Nothing, opposite Robert Stephens, but she came to wider attention when she secured the title role as the teacher in “The Prime of Miss Jean Brodie” (1969), for which she won the Best Actress Oscar.

“My girls are the crème de la crème!” Smith’s Miss Brodie is fond of announcing, in her haughty pronunciation that turns “girls” into “gels.” Smith unleashes all of her most distinctive mannerisms here, keeping her eyes half-closed and placing her body at various angles as she ensorcells her “gels” with all of her heartfelt affectations, dizzying them with her romantic presentation of herself, which hides mysterious and harsh depths of feeling underneath.

Miss Brodie was a role that called upon all of Smith’s resources as an artist, and the moving and frightening thing about this performance is how Smith shows us that Miss Brodie is hiding a weak character underneath her own performance of a strong character; in the end, she is fairly shameless about this, taking up this performance even after a former student has stripped her bare of all her weapons of evasion.

Even scarier was a brief scene Smith did that same year in “Oh! What a Lovely War” (1969) as a music hall entertainer who delivers a curiously snarly sort of song to get men to join up to fight in World War I. Smith is comic here as her character offers this sexual bait-and-switch, but she is fearsome when the camera comes in close and this woman drops her performing mask after she has gotten enough men to sign away their lives. The following year, she killed as Ibsen’s Hedda Gabler for Ingmar Bergman in a red-tinged production that focused on the interior pressure on Hedda; this was clearly a height in her theater career.

Smith foundered a bit in the early 1970s, making choices that were too big and doing triple takes when a double take would have sufficed; she always had a weakness for comic slapstick. But she renewed herself on stage in seasons at Stratford in Canada from 1976 to 1980, playing Rosalind and Cleopatra and many other roles she didn’t quite have the nerve to try for London audiences and critics. She won a second Oscar for playing Oscar loser Diana Barrie in “California Suite” (1978), speeding through her Neil Simon lines and getting laughs in a lengthy comic drunk scene.

In her fifties, Smith did some of her finest screen work. She was a hoot as a delusional, snobby housewife in “A Private Function” (1984), and both comic and touching as poor Charlotte in “A Room with a View” (1985), who makes a fool of herself at some length when she insists on paying for a cab and then finds that she can’t part with even a bit of her money. This portrait of shabby gentility was a starting point for what might be Smith’s greatest screen performance: the alcoholic Irish piano teacher in “The Lonely Passion of Judith Hearne” (1987).

Like Charlotte, Judith Hearne is a passive-aggressive mouse of a lady, but this is only her surface, and Smith is always at her very best when she has a role where she can show the very different sides of a human being. Underneath her sniffy propriety, Smith’s Judith Hearne is a romantic and a sensualist, but this only comes out when she locks herself in her room to get drunk. When Judith drinks, all of her many humiliations and disappointments, both large and small, disappear, and she is a young woman again, alive to the pleasure of music, and hopeful for the future. Religion is one of the things that has stifled her the most, and Smith reaches a tragic height here when she breaks into a church and cries, “I hate you!” at the altar in a loud, piercing voice of lament and rage.

And then Smith did an Alan Bennett monologue for TV called “Bed Among the Lentils” (1988) in which all of her great powers of concentration and anger and seething humor were put to the test for a full 50 minutes in which her character, the alcoholic wife of a vicar, speaks about finding sexual fulfillment with a younger grocer. Smith’s delivery here is so coiled with tension, so laced with authoritative rage at the hypocrisy and meanness of the people around her, that it is difficult to even take a breath once you start watching her; the exhilarating negativity of Smith’s artistic viewpoint on life never had richer material to feed on. Michael Palin, her co-star in “A Private Function,” had this to say about Smith herself: “There’s an intensity of animosity sometimes, which comes out in her acting and can be quite chilling. Maggie in a bad mood is clearly a few degrees worse than most people in a bad mood.”

In the 1990s, Smith sometimes took supporting parts in feature films, like her voyeuristic Aunt Lavinia in “Washington Square” (1997), and on stage she made a particular impression in the acidic and wordy dramas of Edward Albee. On TV, she was simultaneously poisonous and frightened as Violet Venable in Tennessee Williams’s “Suddenly, Last Summer” (1993), which showed again that Smith was always at her best when she could play a person with a public and a private self with a large abyss of some kind in between.

Smith was very funny as the frequently sloshed romance novelist in “My House in Umbria” (2003), for which she won an Emmy, and she made appearances in the “Harry Potter” films that won her a new generation of fans and some financial security, but she made her most popular impression of all as the sharp-tongued Dowager Countess on the TV series “Downton Abbey,” which ran from 2010 to 2015.

The Dowager was a kind of apotheosis of Smith’s latter-day image as the bitchiest of matrons, and this was all in good fun, but her full artistry was engaged one last time in “The Lady in the Van” (2015), which she had played on stage. As Ms. Shepherd, an itinerant lady who took up residence in playwright Alan Bennett’s driveway for many years, Smith once again dramatizes the gap between the public perception of a person and their own private world. Smith’s Ms. Shepherd survives by acting as if she is busy and powerful, when, in reality, she has no power at all, a strategy that Smith seems to deeply understand. She has an indelible moment here when she is asked if she is sorry, and she replies, “Sorry is for God.” All of Smith’s own enormous discontent and rage is distilled in her delivery of this one line.

Who was Smith as a person? Brian Bedford once stopped by her dressing room during an intermission of “Private Lives” in the 1970s and asked her, “How are you, darling?” to which she replied, “Oh, darling, one is nothing, off!” Can you hear her say that line, with its tricky rhythm? As a child, and also as an adult, Smith did not much like herself, and so she preferred to pretend to be others, and she certainly did not like what she saw and heard around her, and so her great career is a kind of revenge on life, murderous and righteous. Her image with the public was always basically comic, and she knew that this could be mistaken for seeming frivolous, but Smith was deadly serious in everything she did (except for maybe that period in the early 1970s when she began overdoing everything).

She got a huge laugh on stage in Hay Fever in the 1960s when she said the line, “This haddock is disgusting!” But once everyone knew she got such a huge laugh on this line, people were expecting it too much, and Smith found that she had trouble getting it again. She was an artist, but she was also a worker at a profession, and this could be great fun, but it could also be the cause of great worry. That worry showed sometimes in those sad, sly big eyes of hers, and in the way her small mouth would twist as if she wanted to retreat entirely from life.

Miss Jean Brodie and Judith Hearne. Hedda Gabler and Rosalind. Violet Venable and the Dowager Countess. These are all very different people. But the one thing that all of Smith’s characters shared was an immense passionate store of emotion that often had to be hidden away for various reasons. Smith knew that there could be such a difference between who we are in private, who we are when we are alone, and who we feel we must present for public show that the difference could be maddening, annihilating. She knew that what people are and what they want to be could be comically and tragically different. Maybe she herself wanted to be Veronica East, the beautiful girl who got all the lead roles in school, and she resented the Veronica Easts of this world so much that she held on to that name and that unfair situation her whole long life, as fuel for her creativity.

Smith saw that life is so often a matter of strategizing. Miss Brodie has a strategy that becomes increasingly obvious to see as evil, or close to evil, even if it is entertaining. Her vicar’s wife in “Bed Among the Lentils” releases her rage at the puny, mean-spirited world around her through alcohol and then sex, which seems to sooth her a bit, finally. Judith Hearne needs to drink when she is alone, and Mrs. Delahunty in “My House in Umbria” must drink a great deal in order to see herself the way she wants to be, as a make-up smeared femme fatale. Charlotte in “A Room with a View” would like to seem generous, but she needs to hold onto every bit of her money. Violet Venable wants her son to be remembered as a major poet, but deep down she knows that he was less than that. Diana Barrie married a gay or bisexual man (Michael Caine), but she wants him to see her, love her, look at her when they make love, if only for one night.

When she was young, Smith once wrote a fan letter to J.D. Salinger after reading The Catcher in the Rye. This was before Salinger withdrew from public life, and he actually wrote back to her, but her mother destroyed his letter before Smith could read it. When she went to see her first movie in 1946, her father beat her when he found out. So Smith came from a background that was ruthlessly anti-pleasure, and she escaped it.

She used to drive Edith Evans crazy by playing her Supremes’s record “Baby Love” over and over backstage during Hay Fever, and she went for a very sensual husband in Robert Stephens and paid a price for it. There was a second marriage, much steadier, to the writer Beverley Cross, who died in 1998, and then survival of illness and continued work and all the attention that came from her late-in-life popularity on “Downton Abbey.” It was fitting that in 2019, for her last appearance on stage, she played Joseph Goebbels’s secretary in A German Life, a one-woman show in which she dramatized the ultimate danger of personal compartmentalization.

In thinking about Smith’s achievement as an actor, there is finally a locked door at the center, a place that says, “Keep out.” That’s why watching her and thinking about her work will always be seductive. The general public could and did respond to her surface image as the grande dame of the put-down, but others can dive deeper into the complexity of her point of view, especially those who were lucky enough to see her on stage at Stratford in the late 1970s. This is a major loss.