Which pope was exhumed twice and buried three times in the ninth century?

...Stephen VI's reasons for what happened next are clearly political when viewed through the lens of history. At the time Stephen VI accused Formosus of perjury, breaking canon law, coveting the papacy and illegally serving as bishop. His hatred for Formosus was so strong that he ordered his body exhumed and put on trial.

The farce that followed is known as the Cadaver Synod and is one of the more bizarre episodes in papal history. The corpse of Formosus was dressed in papal vestments and taken to court where he was interrogated by Stephen VI. Speaking in defense of Formosus was a deacon who, understanding his place in the proceedings, said very little.

It may come as no surprise that Formosus was found guilty on all counts; he was deemed unworthy to have been pope and his corpse was stripped of the papal vestments, his consecration fingers were chopped off and his body dropped in the Tiber where it was rescued by his supporters and secretly buried. By the end of the ordeal, Stephen had fallen out of good graces and was imprisoned then strangled in his cell.

Over the next two years, with the blessing of a new Holy Roman Emperor and three successions of popes, Formosus was cleared of all charges and his body was eventually given a pope's burial and interred in St. Peter's Cathedral.