A founder of a wiki is simply the person who first proposed that the wiki be created. Founders do not have any authority within the wiki to overrule the communities that form there, and they do not own the wiki that they founded.
Founders are automatically given administrator and bureaucrat access to their wiki, but the purpose of this is to allow them to clean up vandalism more easily, not to give them control over the content.
Any other registered user of a wiki can also become an admin, either by asking the founder, or by contacting Wikia (or another bureaucrat, if any) if the founder is inactive. (See the Administrators page.)
Contacting wiki founders
The founder of a wiki is listed on Central Wikia's description page for that wiki and may be named somewhere in the wiki itself.
If you are logged in and have a valid email address in your preferences, you may be able to contact a founder of a wiki using the email this user link on their user page. This will work only if they have a valid email address set in their preferences. You can also click the link to their user page, then click "discussion" and leave them a public message there.