Harry Potter star John Lithgow struggles to 'contemplate' how long he'll be playing Albus Dumbledore John Lithgow will play Albus Dumbledore in the upcoming Harry Potter series on HBO. 6 April 2026 John Lithgow admits playing Albus Dumbledore until he's almost 90 is "an extremely difficult thing to contemplate". John Lithgow as Albus Dumbledore in Harry Potter The 80-year-old actor has signed on to play the Hogwarts headmaster in HBO's upcoming Harry Potter reboot, which will start this Christmas and run for seven seasons, with each one covering one of JK Rowling's books in the wizarding saga.