When a player reaches level 20, he can choose if he wants to stay as a player, perhaps as a peer or if he wants to become a wizard.
Wizards can enlarge or modify the world, add new areas or update old ones.
Such projects can be done in domains, where several wizards work on the same project. It is also not required for a wizard to make any modifications to the game. There can be a lot of social, organisatory and other aspects of wizardly life one can engage oneself in. They improve and modernize the core mudlib and they are in question for important decisions about the mud and the gameplay. They can also help you with questions about coding or in case that a bug occurs.