“A great many changes, but there we are,” Elizabeth says, swatting away an underling’s compliments. “Age is rarely kind to anyone.”

The swap is also something of a gamble for a series that achieved rapturous acclaim for its principal actors, notably Foy, who won a Screen Actor’s Guild award and was nominated for an Emmy. But Morgan and his producers found a pretty sure casting bet in Colman, who is adored by the British public, and last year found broader fame when she won an Oscar for her portrayal of another English queen (Anne) in “The Favourite.” (There is at least one person who didn’t approve of the choice: Charles Moore, a well-known journalist and Margaret Thatcher biographer, wrote in The Daily Telegraph that Colman’s “distinctly left-wing face” made her unsuitable for the part.)

“Olivia has a similar, uncannily intuitive understanding of the role, and a stillness that Claire has,” Suzanne Mackie, an executive producer on the series, said in a telephone interview. “They feel like everyday women, that we should somehow know them, yet as they become the sovereign, they become unknowable and aloof.” (In a review of the new season, The Independent wrote that “there is something dazzlingly banal” about Colman’s portrayal of Elizabeth.)

Colman, who plays a more experienced ruler with a chillier, more confident mien, said in a sit-down interview last fall that she was trying not to think about following in Foy’s footsteps. “I am a massive fan; Claire was just breathtaking in that part,” she said. Sounding rather like her character, she added, “But you just plow on.”

Ben Caron, a director and executive producer on the show, said in a telephone interview that it had been “pretty terrifying” for the new cast. “Not only do you have the real-life ghost of the character, you have the ghost of the previous actor,” he said.