Cobra Dragons are an obscure branch of the dragon family tree in Dungeons & Dragons, having only appeared in the article "The Dragon's Bestiary: All Dragons, Great and Small" for Advanced Dungeons & Dragons 1st Edition.
According to what little lore we have for them, cobra dragons are said to be an evil dragon race native to "the Orient", with a specific setting called out in that they inhabit the realms of Kara-Tur in the Forgotten Empire. Specifically, they're said to be found in the far southern reaches of the T'u Lung Empire, though they are also reputed to dwell in lands to the south and west of T'u Lung. They favor caves and subterranean lairs in tropical and subtrropical regions, though they dislike swamps.
As their name suggests, cobra dragons look like a bizarre combination of a gargantuan cobra and a dragon... in fact, stick a dragon's wings and legs on a giant cobra with black scales offset by an orange underbelly, and you have a cobra dragon in a nutshell. Unlike other true dragons, they have no innate arcane powers, but are all but impervious to hostile magics. They do still maintain a breath weapon - a two-pronged assault of a gout of burning flames followed by a dense cloud of blinding, choking, acrid smoke that acts as a defensive shield for the cobra dragon - and can also attack with flailing claws, a whip-like tail, and lethally poisonous fangs. They are impervious to fire attacks, but extra vulnerable to cold attacks.
They are fiercely territorial, especially around their own species, tolerating each other only during the spring mating season. During this seas, young adult and adult stage cobra dragons seek each other out, wrestling and spitting flames as they assess each other as a worthy breeding partner. Older cobra dragons don't participate in the mating ritual, and actively boast of having outlived the "messiness" of that stage. Weirdly, cobra dragon numbers aren't impeded by this dearth of breeding, and legend has it that a king cobra which lives to a sufficient age will spontaneously transform into a young cobra dragon. Of course, it helps that female cobra dragons are actually quite devoted to protecting their eggs.
Unlike normal dragons, cobra dragons aren't that interested in wealth. They prefer to amass collections of skulls, especially those of powerful, monstrous or rare creatures - humanoid skulls are deemed of little value; the real hot commodities are skulls of dinosaurs, Dire Animals such as cave bears, giants, unicorns and especially those of other dragons. The offering of a rare skull as a gift when attempting to converse with a cobra dragon aids considerably in gaining the dragon’s favor.
Once they hit adulthood, cobra dragons often develop small followings of intelligent slaves that eagerly serve the powerful dragons as almost living gods. Lizardfolk, gargoyles and bakemono are particularly common followers.