Guild Master

The Guild Master - as the title suggests - is the acting head of an officially recognized guild.
I honestly don't know why you bothered looking at this page, as each guild handles affairs in their own way and guild masters are created or removed based on whatever hierarchy system is in place. Maybe you just forgot what a guild master was and somehow skimmed over both the word "Guild" and "Master" when trying to piece it together? I don't know.
There's a list of currently known Guild Masters on the side of the page. There's a good chance that if you're looking at this page, you're really looking for a guild master.

Current Guild Masters:
Kingdom of Acarius
Muntadi Strongjaw - Adventurer's Guild
Stew - Cartographer's Guild