Groovy Gregory is a black man with a large afro in a tacky pink (yellow in Serious Sam 1) 70s disco outfit, complete with stars on the bottom of his feet. In Serious Sam HD and Serious Sam 3: BFE, his back has Serious Sam's logo with red large lips on it, reminiscent of old racist stereotypes of black people.
Groovy Gregory, along with his brother Dancing Denzell, formed the popular “Venilli Manilli” band back in the 20th century. However, their fame ended when it was discovered that Serious Sam was the one who sang their songs and that they were just lip-syncing. Even though their career was over, Sam liked them and their style, so he allowed them to fight with him against Mental's forces.