Adams was born on June 8, 1957 in Windham, New York, the son of Paul and Virginia (née Vining) Adams. He has described himself as "about half German" and also has English, Irish, Welsh, Scottish, and Dutch ancestry. In 2016, Adams said he had a small amount of Native American ancestry, but later discovered via 23andme genetic testing that he does not have any detectable Native American genetic markers. He was a fan of Peanuts comics while growing up and started drawing comics at age 6. He won a drawing competition at age 11.
