Rubeus Hagrid
In "Harry Potter and the Philosopher's Stone", Dudley is given a pig's tail by Rubeus Hagrid which has to be removed at a private hospital in London. In "Goblet of Fire", the Smeltings school nurse advises the Dursleys to put him on a strict diet. During the summer when this diet is enforced, the Weasleys arrive at Number 4, Privet Drive to pick Harry up for the Quidditch World Cup, and Fred Weasley "accidentally" drops a Ton-Tongue Toffee, which enlarges Dudley's tongue to four feet long before his hysterical mother reluctantly allows Arthur Weasley to shrink it. By the start of "Order of the Phoenix", Dudley has been on his diet for a year, taken up boxing, and become a regional inter-school champion.