Sir William Lockhart of Lee (1621–1675), was a Scottish soldier and diplomat who fought for the Covenanters during the 1638 to 1651 Wars of the Three Kingdoms.

Captured at Wigan in 1648, Lockhart was released in 1649 but excluded by the Kirk Party when they invaded England in order to restore Charles II.

[2] After his first wife Martha Hamilton died in 1654, he married Robina Sewster, whose first husband had been distantly related to Oliver Cromwell; they had five sons and two daughters.

These included Cromwell, Julius, killed at Tangier in 1680, Richard and John, who died without issue, and James, who ultimately succeeded.

Their two daughters were Martha, maid of honour to Princess Mary, and Robina, who married Archibald Douglas, 1st Earl of Forfar.

[3] Lockhart reportedly ran away from school when he was 13 and made his way to Danzig, where his relative Sir George Douglas was Ambassador to Poland.

[4] Appointed lieutenant-colonel in the Earl of Lanark's regiment, he served in the Covenanter army that campaigned against Montrose, Royalist commander in Scotland.

In December 1647, Charles agreed to impose Presbyterianism in England for three years and suppress the Independents, but his refusal to take the Covenant himself split the Scots.

He was released after paying a fine of £1,000; he returned to Scotland but the 1649 Act of Classes passed by the Kirk Party banned former Engagers from political or military office.

Lockhart urged on Turenne the necessity of proceeding immediately to the siege of Dunkirk, but this was delayed till June 1658, by which time the Spaniards had strongly entrenched their position.

The town was surrendered on 15 June, and on the 24th handed over to Lockhart, who was made governor by Cromwell, and proceeded to put it in a state of defence.

He took part as the English plenipotentiary in the negotiations which resulted in the treaty of the Pyrenees, and immediately on its conclusion went to England, where he had an interview with George Monck.