Edgar is an Old English name historically associated with the tenth century English king known as Edgar the Peaceful, and there was also a King Edgar of Scotland.
Edgar has been a stalwart on the US popularity lists, never falling below the Top 400 since records have been kept. He now ranks at Number 286, especially popular (as is Edgardo) with Latino families.
Edgar plays a key role in King Lear, and has had several distinguished namesakes, including artist Degas, Edgar Allan Poe, and Tarzan creator Edgar Rice Burroughs. In terms of style, however, most would rate it a distant third to Edward and Edmund.
Trivia tidbit: Joan Rivers' daughter Melissa named her son Edgar after her father, but he is called by his middle name Cooper.