Dimetrodon was a "mammal-like repile", properly known as a Synapsid, that was one of the largest predators of its time, at around 10 feet. It had two different kinds of teeth, canines and shearing teeth, unlike previous reptiles.
Dimetrodon lived in a arid scrubland. The climate was likely similar to modern Texas, which acually the area it roamed. It hunted animals like the similar-looking Edaphosaurus, and probobly didn't have any preadators.