He was called "BA" or Big Arms when he played football in college, i saw some pics of him from high school, his arms were at least very close to 20 inches then
He was given a free membership to Metro Flex because the owner saw him with his veins visible through the spandex, even before he started training for bodybuilding. Apparently people tried to out-lift him and suffered massive injuries and some people were said to have died from trying to best him in lifting.
All gorilla jokes aside, and they are hilarious, Ronnie Coleman was probably the most genetically gifted bodybuilder for mass and strength that the sport has ever seen.