From the first page...
The purpose of this publication is to provide the DM with a number of pregenerated nonplayer characters who can be inserted into any AD&D game campaign.
From the back of the book...
They say that it's hard to find good help these days, but no DUNGEON MASTER will ever have a problem as long as he can draw upon the Rogues' Gallery. Look within and you'll find all manner of non player-character warriors, wizards, priests, and rogues with all their class variations, fully developed and ready to drop into any AD&D campaign. Each of the characters is detailed in the standard, convenient Monstrous Compendium format - including an illustration - with a biography including his or her favorite combat tactics, regular hang- outsm likely cohorts, and much more.
NPCs have lives too; give them more than just a number when they next meet and challenge your adventuring party! Visit the Rogues' Gallery and hire some good help.