Sir Thomas Cavendish (1560 – May 1592) was an English explorer and privateer known as "The Navigator" because he was the first to deliberately attempt to emulate Sir Francis Drake, raiding Spanish towns and ships in the Pacific and then returning by circumnavigating the globe. Though Magellan-Elcano, Loaísa, Drake, and Loyola had all preceded him in circumnavigating the globe, Cavendish's own successful voyage, between 1586 and 1588, was the first deliberately planned circumnavigation. It made him rich from captured Spanish gold, silk, and treasure from the Pacific and the Philippines, with his richest prize being the 600-ton Manila galleon Santa Ana (also called Santa Anna). He was knighted by Queen Elizabeth I of England after his return. He later set out for a second raid and circumnavigation but was not as fortunate and died at sea in 1592, at the age of 31.

Cavendish was baptized on 19 September 1560 in St Martin's Church, Trimley St Martin, Suffolk. He was the third son of William Cavendish and Mary Wentworth. When his father died in 1572, Cavendish inherited a sizeable estate and was placed under the guardianship of Thomas Wentworth, 2nd Baron Wentworth. Wentworth was required to ensure that the boy was prepared for a university education.

In the spring of 1576 at the age of 15, he entered Corpus Christi College, Cambridge but left in November 1577 without taking a degree. He then entered Gray's Inn, London, and for the next several years maintained a lavish lifestyle, making connections in London society including the royal court. He also came to know Richard Hakluyt and others in his circle who were advocating for the English colonization of North America. Cavendish gained a reputation as a spendthrift and between 1583 and 1585 he was taken to court for non-payment of debts.

In the 1580s, Cavendish looked for advancement under the patronage of Walter Raleigh. Raleigh and the Earl of Pembroke helped Cavendish to become a member of parliament representing the borough of Shaftesbury in 1584. In turn, he supported Raleigh's efforts to assume Humphrey Gilbert's contract to colonize America. Cavendish also studied navigation under the direction of Thomas Harriot at Raleigh's Durham House in Westminster.

In 1585, Cavendish was appointed second-in-command to Richard Grenville on an expedition to establish Roanoke Colony in Virginia. He invested in the purchase and provisioning of the fleet that left Plymouth on 9 April 1585. The ships were scattered by a fierce storm but Cavendish's ship, Elizabeth, survived and reached the rendezvous point in Puerto Rico. Grenville was impressed with the navigational skills displayed by Cavendish on his first voyage.

Grenville and Cavendish spent several weeks in the Caribbean gathering supplies for the new colony. They were able to purchase supplies from the Spanish on Hispaniola and also seized two Spanish ships that they encountered along the way. In late June they reached the Outer Banks in present-day North Carolina, where the Roanoke colony was established.

Cavendish returned to England in August aboard the Tyger without profit from his investments but he did gain important experience and several close friends.

By July 1586, Spain and England had become embroiled in the Anglo–Spanish War, which would culminate with the Spanish Armada and its threatened invasion of England in 1588. Cavendish determined to follow Sir Francis Drake by raiding the Spanish ports and ships in the Pacific and circumnavigating the globe. After getting permission for his proposed raids, Cavendish built a 120-ton sailing ship with eighteen cannons, named the Desire. He was joined by the sixty-ton, ten-gun ship Content and the forty-ton ship Hugh Gallant.