Gunter
Doctor Medicine’s bound aberration. He has always been a Slaad. Doctor Medicine has always been a Great Old One Warlock — which means he was never going to summon a fey, and Gunter was never a fey spirit. It was always going to be this. Gunter is a Slaad, Doctor Medicine confirmed in Session 13, and has always been a Slaad. The DM agreed. This makes sense given that Doctor Medicine has always been a Great Old One Warlock.
He arrives when called, does what is asked, and goes back wherever Slaadi go between summons. Whether he enjoys the work is not in question.
First called in Session 9 to deal with the chardalyn warriors charging the crowd. Always been a Slaad then too.