1071: William FitzOsbern
As one of William the Conqueror's closest supporters, FitzOsbern had a key role in preparing for the Norman Invasion and in the Battle of Hastings itself. As reward for his service he received the Isle of Wight and the earldom of Hereford, which were significant points for the defense of England. He continued to serve William in positions of high responsibility, founding abbeys in Normandy and introducing to Hereford the laws of Bréteuil, which became the model for many British boroughs.
In 1071 FitzOsbern went to Normandy to assist Queen Matilda, where he became involved in the dispute over the Flemish succession and was killed at the Battle of Cassel.
The illegitimate son of Roger, Duke of Apulia, Tancred was imprisoned for insurrection against his uncle, William I of Sicily, and later exiled when he attempted yet another coup. Forgiven his rebellion by William II, he led an expedition against Alexandria for the king and commanded a Sicilian Fleet. When William II died without any direct heirs, Tancred became a serious contender for the throne. The feudal barons opposed him, but Tancred had the support of the people of Sicily and of the Pope Clement III. He was crowned king of Sicily in 1190.
Tancred's brief reign was disrupted by King Richard I of England, who demanded a legacy promised him by William II, then provoked a riot and viciously put it down to blackmail Tancred into delivering. Tancred acquiesced, and Richard departed, but soon Holy Roman emperor Henry VI invaded, claiming a right to the throne because his wife Constance was the daughter of King Roger II, Tancred's grandfather. Tancred repulsed Henry's attack, but three years later Henry returned. Before the emperor reached Sicily, however, Tancred died suddenly, leaving a young son, William III. The barons swung their support to Henry, who promised Tancred's family safe conduct but instead imprisoned them in Germany, where William died under questionable circumstances.
1408: Henry Percy, Baron of Northumberland
Northumberland was instrumental in the abdication of Richard II and the accession of Henry IV. However, over the years his loyalty to Henry changed when adequate funds were not forthcoming from the king. He allied himself with Owen Glendower of Wales, issued a declaration that Henry had acquired the crown by fraud, and, raising a large force, rebelled against the king. Missing the disastrous battle himself, he repledged his oath of fealty to Henry, then re-allied himself with Glendower in another doomed rebellion. Northumberland then fled to the Netherlands but returned for one more attempt at overthrowing Henry, and was killed in the Battle of Bramham Moore.
1431: Pope Martin V
As the first pope to reign over a united church after the Great Schism, Martin V had many problems left by the schism to address, and was most successful in restoring Rome. He was inhibited in going forward with plans for reform by his fear of calling a council that might undermine the authority of the papal office.