Sir Humphrey Gilbert (c. 1539 – 9 September 1583) of Compton in the parish of Marldon and of Greenway in the parish of Churston Ferrers, both in Devon, England, was an adventurer, explorer, member of parliament and soldier who served during the reign of Queen Elizabeth I and was a pioneer of the English colonial empire in North America and the Plantations of Ireland. He was a uterine half-brother of Sir Walter Raleigh and a cousin of Sir Richard Grenville.
Gilbert was the fifth son of Otho Gilbert of Compton, Greenway and Galmpton, all in Devon, by his wife Catherine Champernowne. His brothers Sir John Gilbert and Adrian Gilbert, and his half-brothers Carew Raleigh and Sir Walter Raleigh, were also prominent during the reigns of Queen Elizabeth I and King James I. Catherine Champernowne was a niece of Kat Ashley, Elizabeth's governess, who introduced her young kinsmen to the court. Gilbert's uncle, Sir Arthur Champernowne, involved him in the plantation of Ireland between 1566 and 1572. Gilbert's mentor was Sir Henry Sidney. He was educated at Eton College and the University of Oxford, where he learned to speak French and Spanish and studied war and navigation. He went on to reside at the Inns of Chancery in London in about 1560–1561.
Gilbert was present at the siege of Newhaven in Havre-de-Grâce (Le Havre), Normandy, where he was wounded in June 1563. By July 1566 he was serving in Ireland under the command of Sir Henry Sidney (then Lord Deputy of Ireland) against Shane O'Neill, but was sent to England later in the year with dispatches for the Queen. (See Plantations of Ireland and Tudor conquest of Ireland). At that point he took the opportunity of presenting the Queen with his A Discourse of a Discoverie for a New Passage to Cataia (Cathay) (published in revised form in 1576), treating of the exploration of a Northwest Passage by America to China. Within the year he had set down an account of his strange and turbulent visions, in which he received the homage of Solomon and Job, and their promise to grant him access to secret mystical knowledge.
After the assassination of Shane O'Neill in 1567 he was appointed Governor of Ulster and served as a member of the Irish Parliament. At about this time he petitioned William Cecil, Queen Elizabeth's principal secretary, for a recall to England citing "for the recovery of my eyes", but his ambitions still rested in Ireland, and particularly in the southern province of Munster. In April 1569 he proposed the establishment of a presidency and council for the province, and pursued the notion of an extensive settlement around Baltimore (at the southwest tip of modern County Cork), which was approved by the Dublin council. At the same time he was involved with Sidney and Sir Thomas Smith, the secretary of state, in planning the Plantation of Ulster, a large settlement of the northern province of Ulster, by Devonshire gentlemen.
Gilbert's actions in the south of Ireland played a significant part in the outbreak of the first of the Desmond Rebellions. Sir Peter Carew (d.1575), his Devonshire kinsman, was pursuing a provocative, and somewhat far-fetched, claim to the inheritance of certain lands within the Butler territories in south Leinster. Thomas Butler, 3rd Earl of Ormonde, a bosom companion of Queen Elizabeth's from childhood and head of the Butler dynasty, was absent in England, and the clash of Butler influence with the Carew claim created havoc.