Peter Timotheus Carsten, which is his full name (just called Tim, which is short for Timotheus, after Tarzan had to be replaced) is the leader of the TKKG gang, who are named after the initial letters of their names or nicknames.
Previously, Tim was originally called Tarzan by his friends because of his athletic prowess, but he did not want to be compared with this 'half-finished bodybuilder' after he had seen a very bad movie about him (the change actually came about because the name Tarzan is trademarked).