Nennius

Nennius was a Welsh monk active in the 9th century, traditionally credited with compiling or revising the Historia Brittonum around 829-830. His work is a mixture of historical accounts, legends, and topographical information about early Britain, including the earliest known references to King Arthur. The authorship of the Historia Brittonum is debated, with some scholars viewing Nennius as an editor or compiler rather than the sole author.