Gary Oldman's Oscar his finest hour
British actor Gary Oldman won his first Oscar for his portrayal of Winston Churchill in "Darkest Hour" AFP / Mark Ralston

Gary Oldman's Oscar win on Sunday for his portrayal of Winston Churchill in "Darkest Hour" is a triumph for a versatile actor more used to playing villains and rogues than heroic statesmen.

The 59-year-old British actor, who famously portrayed Sex Pistols star Sid Vicious in "Sid and Nancy" (1986), made his name as a bankable movie star playing antagonists.

He goes to great lengths to develop his characters and ploughed through books, newsreel footage and even sat in Churchill's chair to play the World War II leader as he became Britain's prime minister in May 1940.

Oldman is known for his signature "big" acting -- a very physical, over-the-top style developed for the stage, used to great effect for his villainous cinema characters and retained for other roles.

His portrayal of Churchill in "Darkest Hour" had already landed him the best actor Golden Globe -- and the Oscar, which comes on his second nomination, now seals his reputation as one of the finest actors working today.

"I would just like to salute Sir Winston Churchill, who has been marvelous company on what can be described as an incredible journey," Oldman told the Oscars audience on Sunday.

Previously, he had said he welcomed all the accolades, but that the greatest reward was receiving approval from Churchill's descendants.

"Randolph just loves the portrayal. And he feels, 'Oh, you've captured my great-grandpapa -- the humour, the energy'.

"That's my Oscar, right there," he told CNN.

- Becoming Churchill -

In winning the Academy Award, Oldman defeated a tough field: Timothee Chalamet ("Call Me by Your Name"); Daniel Day-Lewis for "Phantom Thread"; Daniel Kaluuya for "Get Out"; and Denzel Washington for "Roman J. Israel, Esq."

Oldman's prior best actor Oscar nomination came in 2012 for his portrayal of melancholy British agent George Smiley in an adaptation of the John le Carre thriller novel "Tinker Tailor Soldier Spy".

Building the part of Churchill, Oldman said he first concentrated on the voice, feeling that he physically looked nothing like the great statesman.

"He is such an icon and so mythologised, you wonder, can you get past the marble statue and reach the man?" he told CNN.

He was captivated by newsreel footage, noting the energy in Churchill's walk and the sparkle in his eyes, revealing an inner sense of humour.

Oldman toured parliament and Churchill's family homes and sat in the chair he used during World War II.

He noticed fingernail marks on the left arm and scratches from his ring on the right -- history recorded in the furniture -- which he took as signs of the stress Churchill was under, and incorporated it into his performance.

- Breakthrough as Sid Vicious -

Oldman left school at 16 and took a job in a sports shop.

Failing to get into the prestigious Royal Academy of Dramatic Art, he studied at Rose Bruford drama school in southeast London and spent a successful decade in theatre.

He burst onto the screen in 1986 with his critically-acclaimed portrayal of punk rocker Vicious. He lost so much weight to play the Sex Pistols bassist that he was briefly hospitalised.

Oldman rose to prominence as a leading figure in the "Brit pack": the gang of up-and-coming British actors of the 1980s that included Day-Lewis, Colin Firth and Tim Roth.

He played Lee Harvey Oswald in "JFK" (1991), Count Dracula in "Bram Stoker's Dracula" (1992) and starred in "Leon" (1994) and "The Fifth Element" (1997).

He had recurring roles in the Batman "Dark Knight" trilogy and the "Harry Potter" series.

He also tried his hand at writing and directing, winning a host of awards in 1997 for "Nil by Mouth" -- a tale of drink, drugs and violence inspired by his own childhood on a south London housing estate.

Oldman's own father was, he says, an abusive alcoholic who left the family when his son was seven.

The actor had a well-publicised struggle with alcohol himself and it took a 70-hour drinking binge for him to realise his life was lurching out of control.

Oldman is now sober and in his fifth marriage, having tied the knot with Gisele Schmidt in 2017.

He has three sons from previous marriages, though not from his two-year union with actress Uma Thurman.