Hardy, from Cheltenham, Gloucestershire, started his acting career after World War Two with the Shakespeare Memorial Company in Stratford, later the Royal Shakespeare Company.
The RSC said it was “very sorry” to learn of his death and posted a picture from one of his productions.
One of his earliest TV roles was portraying Cassio in Othello in 1955.
He went on to become a household name in the BBC’s All Creatures Great and Small, in which he played senior vet Siegfried Farnon.
Other TV roles included Arthur Brooke in Middlemarch in 1994 and Tite Barnacle in Little Dorrit in 2008.
On the big screen, he was seen in Mary Shelley’s Frankenstein and 1995’s Sense and Sensibility.
Hardy was made a CBE in 1981 for services to acting.
He played Churchill several times, including in Winston Churchill: The Wilderness Years, for which he won a Bafta in 1982.
He portrayed the wartime prime minister for preview performances of The Audience, alongside Dame Helen Mirren, in 2013 before withdrawing from the role.
Most recently, he took the lead role in Winston Churchill: 100 Days That Saved Britain in 2015.
Hardy believed actors were born rather than made, telling the BBC’s Desert Island Discs his ambitions were formed when he appeared as a page boy at a wedding.
“I walked down the aisle with my head held high and as I went, every eye was turned towards me and something inside me said, ‘that’s it, get every eye on you’.”
Hardy died at Denville Hall, a retirement home for actors in the outskirts of London.
(SOURCE: BBC)