Deities & Demigods (1980)

From the back cover:

Deities & Demigods Cyclopedia

Provides the Dungeon Master with Gods, Heroes and Monsters from Myth, Fiction and Legend for use in rounding out an Advanced D&D campaign. Within this book are seventeen pantheons of divinities, each profusely illustrated. Also included are new material on Clerics' conduct and their relationship with their Deities, information on Character mortality and immortality and more!

 From the web:

This printing of Deities & Demigods contains 17 pantheons including the Cthulhu and Melnibonean Mythoi. It is easy to identify the 1st printing as Chaosium is not thanked on the bottom of page 4.

Provides the Dungeon Master with gods, heroes and monsters from myth, fiction and legend, for use in rounding out an Advanced D&D campaign. Within this book are fifteen pantheons of divinities, each profusely illustrated. Also included are new material on clerics' conduct and their relationships with their deities, information on character mortality and immortality, and more!