In Diablo I, the quests are a series of missions (fewer in multi-player) on which the character is sent, and which offer advantages when completed. None of them need to be completed, except the Archbishop Lazarus and Diablo quests, which are the key to finishing the game. Quests add background lore details and most give valuable rewards (even if only when reselling). Quests from the expansion pack, Hellfire, are located here.