Gurosu Seijin - Demongone (episodes 47-50)
Demongone summons no other monsters, it fights Jumborg Ace and Jumborg 9 itself. I say "it" because Demongone is both female and male. It first appears disguised as a human female before revealing itself in female monster form (no horns, femine voice) before switching to male form (horns and masculine voice). In either form Demongone is stronger than any other Gurosu Seijin.