Cædwalla ( ; 659 – 20 April 689 AD) was the King of Wessex from approximately 685 until he abdicated in 688. His name is derived from the Welsh Cadwallon. He was exiled from Wessex as a youth and during this period gathered forces and attacked the South Saxons, killing their king, Æthelwealh, in what is now Sussex. Cædwalla was unable to hold the South Saxon territory, however, and was driven out by Æthelwealh's ealdormen. In either 685 or 686, he became King of Wessex. He may have been involved in suppressing rival dynasties at this time, as an early source records that Wessex was ruled by underkings until Cædwalla.