Tiamat

Tiamat is the draconic deity of intrigue, power, treachery, and tyranny. Her children are the Chromatic Dragons, renowned for their rapacious hungers and lusts for treasure and power. She is part of the diumvarate religion of The Dark Lady and the Bright Lord, along with her "Brother" Bahamut.
Although open worship of Tiamat is rare in Dragonborn society, many Dragonborn towns keep small shrines to the Dark Lady and sacrifice gold and other items to her by casting them into seemingly bottomless wells. She is prayed to for power, wealth, and other things considered unseemly to petition Bahamut for.
Tiamat maintains a lair in Avernus, the first layer of the Nine Hells. Some claim she is imprisoned there, and, although she and her followers scoff at the idea, she is often working to gain a return to Tol.