A bright, creative, and somewhat shy 8-year-old boy and the creator of Bloo who visits Fosters. He almost always seems to know what to do when there is a problem. Mac is generally good-hearted, intelligent and well-meaning and is often the voice of reason among his friends (especially Bloo) when they are about to make a decision. However, his good nature tends to make him somewhat naive. He is very attached to his imaginary friend Bloo and it is shown in episodes such as "House of Bloos" and "Duchess of Wails" that his biggest fear is never seeing him again because Bloo is what keeps him happy and cheerful and vice versa. Mac's greatest vice is sugar as he becomes extremely hyperactive to the point of a rabid mania if he eats any; once in this state, he will often become obsessed with seeking any other source (and will also sometimes run around naked or in his underwear). He also has a crush on Frankie. He is voiced by Sean Marquette