Mac's 5-year-old imaginary friend and best friend who resembles a simple, domed cylinder. Bloo is sometimes self-centered, egotistic and narcissistic almost to the point of psychotic delusion and has a knack for getting into trouble. However, he still has a good heart and apologizes for his actions. Bloo loves paddleballs even though he can't make the ball hit the paddle (though the only time he was able to do it was in the episode "Let Your Hare Down"). His full name is "Blooregard Q. Kazoo". He became increasingly mischievous over the run over the series and is shown to have bad memory some of the time. He is voiced by Keith Ferguson.

We all love Bloo. He is the life of the show, the jelly on the peanut butter sandwhich, the sprinkles on the cupcake. Without him Foster's Home for Imaginary Friends would be nothing.