What breed did the Thoroughbred descend from?

Answer 1

The thoroughbred breed descended from three foundation Arabian sires, the Byerley Turk, the Darley Arabian and the Godolphin Arabian. In turn, these three sires produced four main thoroughbred lines: Eclipse, Herod, Matchem and a son of Herod named Highflyer.

The sires would have been bred to the native English stock, which most likely would have included breeds such as the Norfolk Roadster, the Irish Hobby, and the Galloway crossed with Spanish and Italian bloodlines.