A WikiGnome is a person who performs small edits on a wiki to continually improve its overall quality.
(A WikiGnome is also often known as a WikiGardener.)
WikiGnomes are important to the success of a wiki because their edits increase the value of everyone else's content, such as:
WikiGnomes tend to be self-selecting. They're people who care about attention to detail, are offended by messiness and will make the small edits that are required to continually improve the quality of your wiki.
So if you can't select them, how do you increase gnome-like behaviour?
They are the opposite of WikiTroll, who generally try to get a reaction from the community by posting strongly controversial content or doing disruptive things, like deleting someone else's edits. This rarely happens in environments where users are not anonymous and are associated with their edits.
Let's say you're the Champion in your organization and someone from one of the groups you've introduced to the wiki asks:
“Our wiki is used frequently. After a while it gets disorganized and needs a big cleanup - how can I improve this?”
Suggest that team members spend one regular session (perhaps once a week) acting as WikiGnomes. It might also be useful for the group to look for a volunteer willing to act as a sort of head WikiGnome or Maintainer who ensures that pages are up to par.