In 1974, he enjoyed a small role aboard the Horror/Mystery that was The Beast Must Die from Amicus Productions.
In 1999, he earned a bit more screen time as one of the folks troubled by Tim Burton's Sleepy Hollow.
In 2004, he definitely put both feet into the Fantastic with a plum role aboard the fondly-remembered Sky Captain And The World Of Tomorrow.
... but it was in 2005 that he took on the big part of 'Albus Dumbledore' in the Harry Potter franchise, and this likely the work for which he'll be lauded by fans of a certain generation. In this property, he served up some excellent acting in Harry Potter And The Goblet Of Fire (2005), Harry Potter And The Order Of The Phoenix (2007), Harry Potter And The Half-Blood Prince (2009), Harry Potter And The Deathly Hallows: Part 1 (2010), and Harry Potter And The Deathly Hallows: Part 2 (2011).
Of course, there were a few others -- quite a few, in fact -- but I'm perhaps fondest of what the man could do on screen with his appearance as 'Kazran Sardick,' the Eboneezer Scrooge of Doctor Who's delightful "A Christmas Carol," arguably one of that franchise's very, very, very best holiday specials.
Prayers are extended to the family, friends, and fans of Mr. Gambon. May he forever rest in peace.