Douglas was born and raised in the heart of a rough neighborhood in Antioch, California, along with his twin brother Damion, by their parents who worked for steel mills.

Both of them began learning the martial arts from a young age and were taught at home by their father, Danny, who was a black belt in Tae Kwon Do.

Douglas made his professional boxing debut in 2016 against Jasper McCargo, losing via third round knockout.

Douglas got his nickname "Tarzan" from Cesar Gracie while training together, due to his long hair and lanky build.

David's twin brother, Damion Douglas, is also a mixed martial artist who competed for Strikeforce.