where was he from?
Wales or the Welsh Marches
Geoffrey of Monmouth
Geoffrey was born between about 1090 and 1100, in Wales or the Welsh Marches. 
who wrote the first book about king arthur The familiar literary persona of Arthur began with Geoffrey of Monmouth's pseudo-historical "Historia Regum Britanniae" who was this king? He was a legendary British leader who, according to medieval histories and romances, led the defence of Britain against Saxon invaders in the late 5th and early 6th centuries. where did he get his name from? The most widely accepted etymology derives it from the Roman "nomen gentile" Artorius who was the person who wrote about about this king? He was a British cleric and one of the major figures in the development of British historiography and the popularity of tales of King Arthur
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Geoffrey of Monmouth [SEP] Biography
Geoffrey was born between about 1090 and 1100, in Wales or the Welsh Marches. He had reached the age of majority by 1129 when he is recorded as witnessing a charter. Geoffrey refers to himself in his "Historia" as "Galfridus Monemutensis" (Geoffrey of Monmouth), which indicates a significant connection to Monmouth, Wales, and may refer to his birthplace. His works attest to some acquaintance with the place-names of the region. Geoffrey was known to his contemporaries as "Galfridus Arturus" or variants thereof. The "Arthur" in these versions of his name may indicate the name of his father or a nickname based on his scholarly interests.