[2] The Percys had been the leading family in Northern England for centuries, and one of the richest, a combination that made them both essential to a stable regime, and dangerous.

His ancestors included Henry "Hotspur", who led two rebellions, and died at Shrewsbury in 1405; his great-uncle was executed for treason in 1537, as was his uncle, the 2nd Earl of Essex, in 1601.

His position as Lord High Admiral also helped secure the Royal Navy, a decisive factor in winning the war.

Before her death in 1637, they had five daughters, two of whom lived to adulthood; Anne (died 1654), and Elizabeth (1636–1718), who married Arthur Capell, 1st Earl of Essex.

[4] In 1618, he and his tutor, Edward Dowse, began a six-year tour of Europe, including visits to the Dutch Republic, Italy, and France.

[3] Throughout the early 1630s, the 10th Earl attempted to ingratiate himself with Charles I's court, initially unsuccessfully, although his family connections in the queen's household did manage to get him admitted to the Order of the Garter in 1635.

Northumberland attempted to initiate naval reforms, often bypassing the lords of the admiralty and submitting his proposals directly to Charles I and the Privy Council.

[3] In response to the rise of the Scottish Covenanters, who opposed the attempt to introduce the Book of Common Prayer in Scotland in 1637, Charles I appointed an eight-man subcommittee of the Privy Council to deal with the issue.

In May 1640, Northumberland was one of only two members of a subcommittee of the Privy Council who opposed the dissolution of the Short Parliament, a move that confirmed his break with Wentworth (whom Charles had recently named Earl of Strafford) and earned him the displeasure of the king.

[3] Northumberland's brother Henry was involved in the First Army Plot of 1641, an attempt to rescue Strafford from the Tower of London and to forcibly dissolve the Long Parliament.

[3] His first action in open defiance of royal authority came in November 1641, when he obeyed Parliament's instruction to prepare four ships to take men and arms under parliamentary control to Ireland to suppress the rebellion there.

[3] Northumberland's support for the war wavered shortly thereafter, however, in the wake of setbacks faced by parliamentary forces in 1642–1643; he was also disappointed that Parliament chose Robert Rich, 2nd Earl of Warwick rather than himself as the new Lord High Admiral.

Northumberland would gain a reputation as a supporter of the Scots on the committee – many speculated that this was because Scottish forces were occupying his lands in the north.

[3] In early 1647, Northumberland sided with Edward Montagu, 2nd Earl of Manchester and the Presbyterian party against the Independents as they attempted to draw up terms acceptable to the king.

[3] Northumberland opposed the Vote of No Addresses in January 1648 and backed the continuation of attempts to agree terms with Charles I, along with former members of the Peace Party in the House of Commons, such as Denzil Holles.

Attitudes on both sides hardened following Royalist defeat in the February to August 1648 Second English Civil War and a significant section of Parliament and senior officers of the New Model Army, including Oliver Cromwell, concluded further negotiation with Charles I was pointless.

In December 1648, Pride's Purge excluded those MPs who wanted to continue talks, creating the so-called Rump Parliament which voted to put the king on trial.

He was briefly placed under house arrest in 1655 after John Thurloe accused him of encouraging his northern tenants to participate in the Penruddock uprising.

His return to politics was completed with his service as Lord High Constable of England at Charles II's coronation in April 1661.