"Hooray!!! I'm Irrelevant!!!!"
When Steve became pope in September of 885 he had a largish bee in his tiny bonnet concerning a previous pontiff named Formosus – a man who was more or less Stephen V’s chief political rival. According to Stephen there were very troubling questions about the character, qualities, and qualifications Formosus - so much so that with vigilante enthusiasm Stephen V determined to have these questions answered by Formosus himself. The only slight hitch in the plan (as Stephen well knew) was that Formosus was dead and buried.
Did this deter Steven V?
In a show of single-mindedness that demonstrated both laudable commitment to the cause and laughable consternation Pope Steve ordered Formous’ body to be dug up, dressed up, and set upon a courtroom chair for questioning. That’s right! The corpse of Formosus was subpoenaed and – with a little help from his friends – arrived in court on time. However, as one might expect, the accused had little to say in his defense.
(This is where the story gets really good!)
There was only one little detail that Steve had forgotten about but when it came to light the pope quickly realized that in addition to undoing the legacy of his rival he had also managed to cement his own legacy as a nincompoop, dimwit, birdbrain, and a complete fathead.
Steve had gone to great lengths to declare ALL of Formosus’ acts invalid and he had accomplished his goal apparently forgetting that it had been Formosus who had ordained Steve many years earlier. This meant that Steve had accidentally declared his own ordination invalid, which meant that like Formosus, Steve was not a valid pope… But the plot thickens… Shortly thereafter the Church realized that if Stephen’s ordination was illegitimate making him an illegitimate pope then nothing that Stephen declared as pope should be considered valid or binding including the trial and conviction of Formosus whose reputation and legacy were returned to him. For Steve however, the damage was done and the big pointy hat and popemobile were passed to another.