Antipope Celestine II

https://en.wikipedia.org/wiki/Teobaldo_Boccapecci

Teobaldo Boccapecci or Boccapeconai, Latin: Thebaldus Buccapecuc) was elected pope after the death of Pope Callixtus II on 13 December 1124 and took the name Celestine II, but factional violence broke out during the investment ceremony and he resigned before being consecrated or enthroned in order to avoid schism.