Mac (voiced by Sean Marquette) is one of the main characters in Foster's Home for Imaginary Friends. Mac's voice was high in the series premiere, but became slightly deeper in later episodes. He has brown hair, and wears a dark crimson t-shirt with a white sweater underneath, black and white tennis shoes, a green backpack, and tan khaki pants.
Mac is a bright, unselfish, creative and somewhat whimy kid who created Blooregard Q. Kazoo when he was three years old. Mac is unusually clever and almost always knows what to do when there is a problem. He stands three feet, six inches tall and weighing 67 pounds, and is a 5th grader, and is Terrence's 11 year old brother, and his birthday is on December 8th (according to his Coco Card) with a sense of reason and somewhat large vocabulary to match. He tends to be the one to settle any mishaps that the imaginary friends (particularly Bloo) end up causing. Mac is usually very good-natured, despite Bloo's continuing antics. No matter what happens to Bloo or any other member of the house, Mac is usually the one to bail them out. However, he has been known to snap; Mac has a strongly moral personality and he always avoids doing wrong things, but sometimes he is pushed to do otherwise, almost always by Bloo. That said, he can be very rambunctious and childish when he wants to be, and generally has no problem pulling pranks or messing around with Bloo as long as nobody gets hurt. Some episodes also have him be more naive and childlike than usual, like "Adoptalypse Now" or "Fools And Regulations." There is nothing that he loves more than visiting Foster's and spending time with his friends. Foster's creator Craig McCracken said in an interview that Mac was based on his childhood at the age of seven following his father's passing. He also has a crush on Goo but Adam and Douglas the only two nerds who have a crush on Frankie.
- Mac will meet Jeffrey, Jaden, Sonic, Hiccup and their friends in Jeffrey, Jaden & Friends' Storm Adventures of Foster's Home for Imaginary Friends: Destination Imagination.
- Mac will meet the Cyberchase Fighters in Michael Buzz and Delete's Adventures of Foster's Home For Imaginary Friends: Destination Imagination and join the Cyberchase Fighters at the end along with Bloo, Wilt, Eduardo, and Coco.