Sean Weasel McGee is a crew member of Diseased Productions and is the one who contributed to the creation of the Thing-Thing series, He has also appeared as a civilian in The Chronicles of Stinky Bean who gives the protagonist a minigun-like weapon in the part where you fight a rogue Thing-Thing (inferred to be Project 154).
His cartoon-drawn face also appears in the poster in 'Moron Marathon' with words such as "Game producers are NOT people!!!" and "Game producer witch hunt" respectively.
It is apparent that Weasel is not fond of people decompiling Thing-Thing without his "consent", as he leaves a picture (shown below) in the game files that addresses those who do. Interestingly, he believes this is because they are attempting to steal assets for their own game, rather than simply looking at sprites and extracting them.
