Property:Last editor is

Change propagation updates are pending (659 jobs estimated) and it is recommended to wait with modifications to a property until the process has been finalized to prevent intermediary interruptions or contradictory specifications.

"Last editor is" is a predefined property that contains the page name of the user who created the last revision and is provided by Semantic MediaWiki. This property is pre-deployed (also known as special property) and comes with additional administrative privileges but can be used just like any other user-defined property.