The Beaufort family were the illegitimate children of John of Gaunt and his long time mistress Katherine Swynford. Eventually the children were declared legitimate and John and Katherine married, though the Beauforts and all of their descendants were specifically barred from succession to the throne of England. This may have reflected the ambitious threat John was perceived to be to the childless Richard II.
The eldest son, John Beaufort, was created Earl of Somerset while the second, Henry Beaufort, joined the clergy, finally being appointed as Bishop of Winchester, created Cardinal Beaufort and serving as Chancellor several times under his half-brother Henry IV and nephew Henry V. Thomas Beaufort was made Duke of Exeter, serving both Henry IV and Henry V before dying without children. The only daughter, Joan Beaufort, married her second husband Ralph Neville, Earl of Westmorland and her children included Cecily Neville, who married Richard Duke of York.
Joan Beaufort's line was to prove significant but it is the descendants of the eldest son, John Beaufort, Earl of Somerset who were to prove instrumental in the Wars of the Roses. John married Margaret Holland, daughter of the Earl of Kent and they had six children. The eldest was Henry who succeeded to his father's earldom but died without children at the Siege of Rouen in 1418. The second son was John Beaufort who became Earl of Somerset on his brother's death. Created Duke of Somerset by Henry VI in 1443, John proved a poor military commander. Eventually, whilst ill in 1443, John mistakenly led a force against a town in Brittany friendly to England. He returned to England in disgrace and died the following year, with rumour growing that he had taken his own life. John had only one child, a daughter, Margaret Beaufort, who became the richest heiress in England and whose impact would be felt keenly some forty years after her father's death.
John's other siblings included Joan Beaufort who married King James I of Scotland and Edmund Beaufort, who succeeded John as 2nd Duke of Somerset and was to come into conflict with Richard of York. This duke had many children; his sons Henry the 3rd Duke of Somerset, Edmund the 4th Duke and John, Earl of Dorset were to become key Lancastrian leaders during the ensuing civil strife.
Margaret Beaufort, daughter of John, 1st Duke of Somerset was placed in the care of the half-brothers of King Henry VI, Edmund and Jasper Tudor. She was married to Edmund Tudor, by who she had her only child, Henry Tudor, later King Henry VII. Margaret was 12 when she married the 24 year old Edmund and she gave birth the following year aged 13. Edmund died before Henry was born and Margaret later married Sir Henry Stafford, son of the Duke of Buckingham and then Thomas, Lord Stanley, later Earl of Derby. Margaret devoted her life to her only son and her drive served to create the Tudor dynasty.
The Neville family were an immensely powerful northern affinity. Alongside, and often in opposition to, the Percy family Earls of Northumberland, the Nevilles oversaw the north of England, far away from the Court in London. Ralph Neville was created Earl of Westmorland by King Richard II in reward for his support against the Lord Appellant in 1397. Ralph Neville first married Margaret Stafford with whom he had eight children. When she died he married Joan Beaufort, daughter of John of Gaunt. Ralph’s loyalties were therefore tested when his king took against his new family. When Henry Bolingbroke landed, Ralph supported him and was in the deputation at the Tower of London that received the abdication of King Richard II.
By his death in 1425, Ralph had a further fourteen children with his second wife, some of who would become significant political figures and would take a substantial role in the Wars of the Roses. His eldest son with Joan was Richard Neville who, via his mother, became 5th Earl of Salisbury. Richard was the father of the Earl of Warwick who was to become known to history as the Kingmaker. Richard's youngest sister, Cecily, married Richard of York, joining the royal family and making the two Richards brothers-in-law. Robert Neville served as Bishop of Salisbury, William Neville, another son, became Earl of Kent after switching allegiance from Lancaster to York. Several of Ralph and Joan's other children formed a large part of the minor nobility in the north.