Sir Humphrey Gilbert (c. 1539 – 9 September 1583) of Devon in England was a half-brother (through his mother) of Sir Walter Raleigh. Adventurer, explorer, member of parliament, and soldier, he served during the reign of Queen Elizabeth and was a pioneer of English colonization in North America and the Plantations of Ireland.
Gilbert was the fifth son born to Otho Gilbert of Compton and Greenway, also Galmpton, and Devon, by his marriage to Katherine 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. Katherine 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 efforts to establish plantations in Ireland between 1566 and 1572.
Sir Henry Sidney became Gilbert's mentor, and he was educated at Eton and the University of Oxford, where he learned to speak French and Spanish and studied the arts of war and navigation. He went on to reside at the Inns of Chancery in London in about 1560–1561.
Gilbert's mottoes, Quid non? ("Why not?") and Mutare vel timere sperno ("I scorn to change or to fear") indicate how he chose to live his life. He 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 Sidney (then Lord Deputy) against Shane O'Neill, but was sent to England later in the year with dispatches for the Queen. (See Early Plantations (1556–1576) and Tudor conquest of Ireland). At that point he took the opportunity of presenting the Queen with his A discourse of a discouerie for a new passage to Cataia (A Discourse of a Discovery for a New Passage to Cathay) (published in revised form in 1576), treating of the exploration of a Northwest Passage by America to Asia. 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, with their promise to grant him access to secret mystical knowledge.