Thematically, nagas seem to be about possession, control, and of holding on overlong to history. Sometimes this is positive—guardian nagas are benevolent lawful good protectors of sacred places, for instance—but often it is greedy, grasping, and covetous. Dark nagas in particular, to quote the Bestiary, “covet luxury, wealth, and power over others.” Like several other dark races (doppelgangers and rakshasas come to mind), dark nagas require both the trappings of power and the validation of those they see as lesser beings. That they so often succeed in acquiring these things is a testament to their cunning and their magic.
The caustic, bitter head librarian of the Scriptorium is a dark naga. He patronizes the nervous clerks and scribes who labor under him as “his moronic hands and feet.” Secretly though, he envies them, and collects magic items and elemental servants of Air that allow him to better manipulate the books, pens, and inks he so loves.
Ashlyssar’s fiefdom is a tumble of elephant-carving-covered ruins in the Pashmedi Jungle. She has managed to convince the local kobolds and she is a goddess and demands tribute payments from nearby catfolk settlements as well. She prefers to avoid most other humanoids, but regards any obvious spellcasters as threats to be snuffed out.
The marchioness of San Markay—secretly a dark naga shielded by illusions and the ruses of loyal advisors—has survived two assassination attempts. She hires sellswords to follow the trail back to its source. If they succeed, she will learn the mastermind is her own sister, similarly masquerading as a merchant lord.
—Pathfinder Bestiary 211
You can find a little more about nagas in the 3.5 Forgotten Realms sourcebook Serpent Kingdoms , but that’s not why you should buy it. You should buy it because it’s awesome.
I picked it up because I’m a sucker for new PC races. But the book ended up being one of my absolute favorites of that era, offering just the right mix of Ed Greenwood setting and story, Eric L. Boyd divine insights and mythology, and Darrin Drader…whatever Darrin Drader did (the crunch maybe?). I’ve returned to it again and again.
Also, Jonathan M. Richards wrote one of the last 2nd Edition Dragon Magazine “Ecology” articles about the dark naga as well as the first 3.0 one for yesterday’s darkmantle.
Edit: Took me long enough to get this up. The original entry was: “Still sick. My lymph nodes have advanced to Huge size and gained the half-fiend template.”