Alexander Leslie, 1st Earl of Leven was a Scottish military officer and peer. Born illegitimate and raised as a foster child, he subsequently advanced to the rank of field marshal in Swedish Army, and in Scotland became Lord General in command of the Army of the Covenanters, a privy councillor, captain of Edinburgh Castle, Lord Balgonie and Earl of Leven. In England he commanded the Army of the Solemn League and Covenant and was senior commander of the Army of Both Kingdoms (1642–1647). Leslie served in the Thirty Years' War, the Bishops' Wars, and most of the English Civil War, fighting primarily in the First English Civil War. Leslie would live a long life, dying roughly at the age of 80 or 81.

Covenanters were members of a 17th-century Scottish religious and political movement, who supported a Presbyterian Church of Scotland and the primacy of its leaders in religious affairs. The name is derived from covenant, a biblical term for a bond or agreement with God.