Frequently Asked Questions Who is the diet Dr Pepper guy? The diet Dr Pepper guy refers to the character known as “Lil’ Sweet” in the diet Dr Pepper commercials. Lil’ Sweet is played by American musician and actor, Justin Guarini. He first appeared in diet Dr Pepper commercials in 2015 and quickly became popular for his flamboyant personality and catchy jingles. Learn more about Lil’ Sweet What is the role of the diet Dr Pepper guy? The diet Dr Pepper guy, or Lil’ Sweet, is the quirky and entertaining mascot of diet Dr Pepper. His role is to promote the…