Conquests of Camelot: The Search for the Grail
Conquests of Camelot is one of a couple of Sierra adventure games designed by Christy Marx (a screenwriter whose credits include creating the Jem & The Holograms cartoon and writing the episode of Babylon 5 about the Holy Grail, to bring us back on-topic). Conquests of Camelot gives you control of Arthur himself, on a quest to find three missing knights and the Holy Grail. Unusually that quest takes you away from England, eventually leading all the way to Jerusalem to meet and learn about legendary figures from other cultures. It's sneakily kind of educational.