By Ryan Parsons | Image property of respective holders.
Though I can't remember the description of Horace Slughorn matching up to Jim Broadbent, I can't help but be excited by his participation in Harry Potter and the Half-Blood Prince.
Jim Broadbent for Harry Potter and the Half-Blood Prince
Horace Slughorn is described as so fat that he can disguise himself as an armchair. Slughorn feels guilt about Voldemort, as it was he who gave Tom Riddle the necessary information on Horcruxes; items that only become important in the final two books. Well, the second book is important, but you don't know this until the sixth.
In the sixth book, Dumbledore gives Potter the task of acquiring a memory from Slughorn that should help reveal what exactly Voldemort learned from the ex-Hogwarts teacher. Horace returns to Hogwarts to teach potions thanks to his admiration for Potter.
The good people at DarkHorizons have discovered that the great Jim Broadbent will take on the role of Horace Slughorn:
Broadbent: Who am I? He's called Horace Slughorn. He's a retired teacher of magic who's drawn back out of retirement because he's got some secrets they need in the battle against the Deatheaters and he's quite star struck as a teacher and he's drawn back into the fold because he likes to notch up celebrity students, and he's drawn back by Harry.
Though Broadbent isn't an exact fit physically, his personality and energy should make him a perfect match.