Vanguard is a group of Fandom users who have volunteered to help make Fandom's content available on the widest possible range of devices and to help communities learn how to use some of Fandom's more technically challenging products. They have been given additional user rights that allow them access to the MediaWiki and Template namespaces, Fandom-wide.
Vanguard members have a few of the same privileges as local administrators, but across all of Fandom. In particular, they can fully access your site's Template and MediaWiki namespaces. They do not replace or "outrank" your local administrators, and Vanguard team members will make every effort to consult with your active and engaged local team. Additional abilities allow classifying multiple templates at once and enabling or disabling features like Europa.