Alexander Henderson (c. 1583 – 19 August 1646) was a Scottish theologian, and an important ecclesiastical statesman of his period. He is considered the second founder of the Reformed Church in Scotland, and its Presbyterian churches are largely indebted to him for the forms of their dogmas and organisation.
He was born at Criech in Fife (possibly Crail). He graduated at the University of St Andrews in 1603, and in 1610 was appointed professor of rhetoric and philosophy and questor of the faculty of arts. In 1615 he was presented to the living church of Leuchars as their minister. As Henderson was located upon his parish by Archbishop George Gledstanes, and was known to sympathise with episcopacy, his settlement was at first extremely unpopular; but he subsequently changed his views and became a Presbyterian in doctrine and church government, and one of the most esteemed ministers in Scotland. He early made his mark as a Church of Scotland leader, and took an active part in petitioning against the five acts and later against the introduction of a service-book and canons drawn up on the model of the English prayer-book.
On 1 March 1638 the public signing of the National Covenant began in Greyfriars Kirk, Edinburgh. Henderson was mainly responsible for the final form of this document, which consisted of
Owing to the skill shown on this occasion he seems to have been applied to when any manifesto of unusual ability was required. In July of the same year he proceeded to the north to debate on the Covenant with the famous Aberdeen doctors but he was not well received. Robert Baillie wrote: "The Voyd church was made fast, and the keys kept by the magistrate".