The Numskulls was originally a comic strip in The Beezer, It then moved to The Beano in 1993 after The Beezer folded. Another version appears in the digital incarnation of The Dandy.
It's been shown that several other Beano characters have their own Numskulls inside their head. Among these were Derek the Sheep and several Bash Street Kids including Plug, Spotty and Cuthbert. Even Fred once used his magic bed to travel inside his own head to discover that his Numskull in charge of his brain has been sound asleep for nearly 5 years.