In 1082 Bishop Odo -the arrogant and extravagant force behind the success of 1066- apparently had serious designs to "become Pope" (even rumoured to have sounded out clerics as to whether there was remote precedent for a bishop becoming king!), causing his final quarrel with his half-brother, king William I, who owed Odo alot and had relied heavily upon him.
Odo knew very well of Pope Gregory VII's troubles in Rome, (ie. being deserted by Cardinals as German Emperor Henry IV threatened Rome militarily), & so he maybe hoped to present himself as an option between Gregory, and Henry's choice- the anti-Pope Clement III- and expecting martial aid from Norman-Sicilians, then beginning to dominate the region?
Since 1070 when he had lost the Archbishopric of Canterbury to Lanfranc (his great rival, as they hated each other personally and politically), Odo must have realised that his ecclesiastical prospects in England were crippled whilst Lanfranc was whispering into his brother’s ear?
At first, from 1080, William – riled by the pope’s ill-advised attempts to get him to acknowledge the Papacy as overlord over England that year- may even have vaguely backed Odo early on in his design to influence the Papacy. But by now Odo had gone too far…
In his pomposity, it seems that he had tried to 'buy' the papacy itself, by offering bribes of coins/letters to the Roman pilgrims and influential noble families in order to smooth his passage to his prospective See there.
He was also planning to guard a newly-bought and lavish palace in Rome with large numbers of Norman knights- who were much-needed for England’s defence at that time, as ordered by his half-brother William.
William- then in Normandy as Odo sailed to England and then prepared to head for Rome from the Isle of Wight- was infuriated by this rebuff of his authority (not to take knights outside of England) and saw this all as the ultimate betrayal (Odo was meant to be William’s regent in his absence!) and dashed back in person to the Isle of Wight.
William questioned Odo’s underlings as to his half-brother’s whereabouts, and found Odo (his men had already made off with much of the stashed treasure- hidden in woods and other places) and had him arrested- put the fallen bishop and secular warrior on trial.
Odo was accused of ‘corruption’ for abusing his rule as Earl of Kent in England as regent whilst William was away (Odo had been brutal, ruthless and arrogant as regent- defending Normans that raped and pillaged, and didn't uphold the 'rights' of the oppressed and dispossessed English).
In 1083 Odo was tried by William as a layman & Earl of Kent and NOT as a churchman (advised by Lanfranc and cunningly avoiding Odo's claims that as a churchman he couldn't be touched), he was imprisoned until released on William's death in 1087- released only against the dying king's wishes.
Odo was not totally disinherited however- in the Domesday book, he was 2nd richest man in England, but years later (1088) after he rebelled against William II in favour of the new king's brother, Robert Curthose, he was deprived of his land in 28 counties and lost his English titles, then finally WAS dispossessed & banished from England by Rufus.
But, partially in Odo's defence- didn't the Papacy demand that bishops and heads of state make such a military pilgrimage to Rome?