Diablo II/Act IV

Halbu
Halbu sells you weapons and armor and can repair your damaged equipment.

Jamella
Jamella can heal you and sell you weapons, armor, potions and scrolls. She can also let you Gamble on her unidentified magic items.

Tyrael
Tyrael is the Archangel who fought Diablo and Baal and crafted the runeblade Azurewrath. He initiates the quests "The Fallen Angel" and "Terror's End."

Deckard Cain
Deckard Cain has accompanied you to Heaven's stronghold to give you advice and to identify your magic items.

Quests

 * 1) The Fallen Angel
 * 2) The Hellforge
 * 3) Terror's End