Deckard Cain is an
NPC inhabitant of
Tristram in the
Diablo series. When Tristram is overrun in
Diablo II, you have to rescue him.
Cain is a wise fellow
1, and he talks alot ("Stay a while, and listen."). He always provides good advice, and will
identify magical items for you, so that you can make use of their special properties. Additionally, he's involved in just about every quest in
both games, and is the sole surviving inhabitant of Tristram at the end of
Diablo II.
1It is later, in D2, that we discover Cain to be one of two surviving members of the ancient Horadrim order. They were the ones who entombed the three Prime Evils (Diablo and his brothers, Baal and Mephisto) in Soulstones. No one knows how old this guy really is.