From the longer Wikipedia page 
Rhys ap Thomas (1449–1525) was a Welsh soldier and landholder who rose to prominence during the Wars of the Roses, and was instrumental in the victory of Henry Tudor at the Battle of Bosworth Field. He remained a faithful supporter of Henry and was rewarded with lands and offices in South Wales. He is also notable for having possibly delivered the death blow to King Richard III at Bosworth with his poleaxe.
Usurpation of Richard IIIEdit
In 1483, Edward IV died. His son, Edward V was still a minor. Edward's surviving brother Richard of Gloucester and the Duke of Buckingham moved to prevent the unpopular relatives of Elizabeth Woodville, Edward's Queen, from sharing in power or even dominating the government during the young King's minority. However, Richard went further, declaring Edward's children illegitimate and seizing the throne himself. The young Edward V and his younger brother (the Princes in the Tower) disappeared and were possibly murdered. Buckingham turned against Richard and led a revolt aimed at restoring the House of Lancaster, in the person of the exiled Henry Tudor, Earl of Richmond, to the throne. The revolt failed. Buckingham himself had raised a force at Brecon in mid-Wales, but storms and floods prevented him crossing the River Severn to join other rebels in England, and his starving soldiers deserted. He was soon betrayed and executed. The same storms prevented Henry from landing in the West Country.
Rhys had declined to support Buckingham's uprising. In the aftermath, when Richard appointed officers to replace those who had joined the revolt, he made Rhys ap Thomas his principal lieutenant in south west Wales and granted him an annuity for life of 40 marks. Rhys was required to send his son Gruffydd ap Rhys ap Thomas to the King's court at Nottingham as a hostage, but he excused himself from this obligation by claiming that nothing could bind him to his duty more strongly than his conscience. He is supposed to have taken an oath that
'Whoever ill-affected to the state, shall dare to land in those parts of Wales where I have any employment under your majesty, must resolve with himself to make his entrance and irruption over my belly.'
Nevertheless, he is presumed to have carried on some correspondence with Henry Tudor, who was preparing another attempt in France to overthrow Richard.
On 1 August 1485, Henry set sail from Harfleur in France. With fair winds, he landed near Dale on the north side of Milford Haven, close to his birthplace in Pembroke, with a force of English exiles and French mercenaries. At this point, Rhys should have engaged him. However, Rhys instead joined Henry. Folklore has it that the Bishop of St. David's offered to absolve him from his previous oath to Richard. The Bishop also suggested that Rhys fulfil the strict letter of his vow by lying down and letting Henry step over him. This undignified procedure might have weakened Rhys's authority over his men, so instead, Rhys stood under the Mullock Bridge north of Dale while Henry marched over it.
Henry's and Rhys's forces marched separately through Wales, with Rhys recruiting 500 men as he proceeded. They rejoined at Welshpool before crossing into England. On 22 August, they met Richard's army near Market Bosworth. In the resulting Battle of Bosworth, Richard launched an attack led by John Howard, 1st Duke of Norfolk. According to a contemporary ballad, Rhys's men halted the assault. "Norfolk's line began to break under pressure from Rhys ap Thomas's men" and the Duke was killed by an arrow shot. (Ralph A. Griffiths and Roger S. Thomas, The Making of the Tudor Dynasty, p.185.) In desperation to kill Henry, Richard charged directly at him. He was unhorsed and surrounded. The poet Guto'r Glyn implies that Rhys himself was responsible for killing Richard, possibly with a poll axe. Referring to Richard's emblem of a boar, the poet writes that Rhys "killed the boar, shaved his head" ("Lladd y baedd, eilliodd ei ben"). (Griffith, Ralph, Sir Rhys ap Thomas and his family: a study in the Wars of the Roses and early Tudor politics, University of Wales Press, 1993, p.43. See also guto'r glyn.net) However, this may only mean that Rhys's group of Welsh halberiers killed the king, since the Burgundian chronicler Jean Molinet, says that a Welshman struck the death-blow with a halberd. Guto'r Glyn himself says that Rhys was "like the stars of a shield with the spear in their midst on a great steed" ("A Syr Rys mal sŷr aesaw, Â’r gwayw’n eu mysg ar gnyw mawr"). He was knighted on the field of battle. (E. A. Rees, A Life of Guto'r Glyn, Y Lolfa, 2008, p.212.)