Forgotten fourth member of the General Foods "horror" cereal trinity that includes Count Chocula, Frankenberry and Boo-Berry.
Fruit Brute was a werewolf. His cereal was relatively short-lived (1974-1982) and arrived after my Mom had banned sugar cereals, so I can't vouch for its quality.
Two strange assertions from that page: 1) Fruit Brute boxes appear in Quentin Tarantino movies; 2) There was a fifth cereal called Yummy Mummy, circa 1988. I can't say that name without laughing out loud, nor does it sound particularly yummy. No wonder it flopped.