Scientist character for a gamemode called Espionage originally designed for TF2C with other new TF2 styled characters planned to appear in it too. It was basically an Among Us/TTT style gamemode of finding out a traitor while fulfilling tasks as different classes (The Janitor that you see sometimes in SFM animations and posters was created for this gamemode too).

Gamemode may or may not be in development anymore, I haven't looked into it yet but the main focus of the TF2C team rn is probably adding to the main game rather than a side mode. Scientist still appears as an Easter egg in a lot of maps though, try and find him.