686 Pessimistic Insight was a Monitor in charge of Installation 02 after the Monitor Civil War. It can be assumed, therefore, that he sided with Guilty Guilty during this conflict but he could just as easily have been one of the Monitors who dropped out of the war.
His ring was attacked by Daleks at some point during Johnny's four year stay in space. The ring was destroyed and, despite his best efforts to contact 049 Abject Testament, Pessimistic Insight was destroyed by the Cult of Skaro. He put up quite a fight, taking down many waves of Daleks before being shot at by Dalek Sec. The enraged Monitor turned his weapon towards Sec but was shot again by Caan, disabling his shields. 686 Pessimistic Insight fired one last shot which impacted the Ring's safety panel, disabling the Flood Containment Facility's shields before he was finally brought down by Sec. The Daleks then had to fight a three way war with the Flood and the Sentinels on the ring before it was destroyed.
His valiant attempt to defend his Installation did not go unrecognised, however, for two reasons. One, the attack on his Installation triggered the Ark to begin constructing replacement parts, which were then used to repair the Ark itself. And also, League scouts later found what was left of Installation 02 and found the security recordings of his last stand. From that they were able to determine that the Daleks destroyed the ring to cleanse the Flood threat there, so that Pessimistic Insight's death would not have been in vain.