Pope Formosus (birth name unknown) was Pope from 6 October 891 to his death in 896. His brief reign as Pope was troubled, and his remains were exhumed and put on trial in the Cadaver Synod.
As Cardinal-Bishop of Portus, he represented the Papacy on a number of diplomatic missions. Shortly after the installation of Charles the Bald as Holy Roman Emperor, fearing certain political repercussions on the part of Pope John VIII, Formosus fled to Tours. Upon refusing a directive to return, he was subsequently excommunicated. The sentence was withdrawn in 878, upon his promising never to return to Rome. In 883, Formosus was reinstated by Pope Marinus I.
Shortly after Formosus' election as Pope, he was asked to intervene in Constantinople, where the Patriarch Photius had been ejected and Stephen, the son of Emperor Basil I, had taken the office. Formosus refused to reinstate those who had been ordained by Photius, as his predecessor, Stephen V, had nullified all of Photius' ordinations. However, the eastern Bishops determined to recognize Photius' ordinations nonetheless.
Formosus also immediately immersed himself in the dispute between Odo, Count of Paris, and Charles the Simple for the French crown; the Pope sided with Charles, and zealously exhorted Odo (then holding the crown) to abdicate on Charles' behalf, to no avail.
Formosus was deeply distrustful of Guy III of Spoleto, the Holy Roman Emperor, and began looking for support against the Emperor. To bolster his position, Guy III forced Formosus to crown his son Lambert as co-Emperor in April 892. The following year, however, Formosus persuaded Arnulf of Carinthia to advance to Rome, invade the Italian peninsula, and liberate Italy from the control of Spoleto.
In 894, Arnulf's army occupied all the country north of the Po River. Guy III of Spoleto died in December, leaving his son Lambert in the care of his mother Agiltrude, an opponent of the Carolingians. In autumn 895 Arnulf undertook his second Italian campaign, progressing to Rome by February and seizing the city from Agiltrude by force on February 21. The following day, Formosus crowned Arnulf Holy Roman Emperor in St. Peter's Basilica. The new emperor moved against Spoleto but was struck with paralysis on the way and was unable to continue the campaign.
During his papacy he also had to contend with the Saracens, who were attacking Lazio.
On 4 April 896, Formosus died. He was succeeded by Pope Boniface VI.