Gregory the Smarmy was a medieval wizarding inventor who created Gregory’s Unctuous Unction, a potion which induces the drinker to believe that the one who gave them the potion is their best friend (FW).
Potion making and inventing
Other canon notes and references
A statue of Gregory the Smarmy stands in a corridor on the fifth floor of Hogwarts; there is a secret passageway behind it leading out of the school (PS9). This corridor was also the scene of Fred and George's portable swamp and subsequent flight for freedom (OP29).