Offa was a powerful Anglo-Saxon king who ruled the kingdom of Mercia in present-day England from 757 to 796. He is known for his military successes and for establishing Mercia as the dominant kingdom in England during his reign. Offa is also famous for constructing Offa's Dyke, a large earthwork that served as a boundary between his kingdom and the Welsh kingdoms to the west. He was a significant figure in early medieval English history and left a lasting impact on the political landscape of the time.