Gwledig translates as emperor. A person holding the title was an arglwyd over-king.
As a ruler over several chieftains, gwledigs were the Briton's first true kings since the arrival of the Romans. Ceredig, a gwledig in the Strathclyde genealogies, is often credited with rule over much of modern Strathclyde.
As an over-king, it was as much his duty to maintain order with his own arglwyd and direct their attacks as it was to raid himself. In true wars, which developed around the same time as the gwledig, he would be able to lead all of his chieftains into battle.
The formation of true kingdoms was a first step in reclaiming the unity the Britons had enjoyed under Roman rule. It also gave them more ability to defend against Germanic incursions.