Sir Thomas Posthumus Hoby (1566 – 30 December 1640), also sometimes spelt Hobie, Hobbie and Hobby, Posthumous and Postumus, was an English gentleman and politician who sat in the House of Commons at various times between 1589 and 1629.
A Puritan, he has been claimed as the inspiration for Shakespeare's character Malvolio in Twelfth Night.
Hoby was the younger son of Sir Thomas Hoby (1530–1566), the English Ambassador to France in 1557, by his marriage to Elizabeth Cooke, who was a daughter of the humanist Sir Anthony Cooke (1504–1576), one of four sisters notable for their learning. Hoby was born after his father's death, which led to his gaining the additional name of 'Posthumus'. His sisters Elizabeth and Anne died within a few days of each other in February 1571, while his elder brother was the diplomat and scholar Sir Edward Hoby (1560–1617). Hoby was also a nephew of Sir Philip Hoby, Master-General of the Ordnance and an English ambassador to the Holy Roman Empire.
Hoby was a very small boy and grew up to be nicknamed "the little knight" for his slightness and short stature. He was educated at Eton and at Trinity College, Oxford, matriculating in 1574 at the age of eight.
Also in 1574, some years after his father's death, Hoby's mother married secondly John, Lord Russell, the eldest surviving son of the Earl of Bedford, and with him had three further children, Elizabeth, Anne and Francis. She was the sister-in-law of William Cecil, 1st Baron Burghley, Queen Elizabeth's Secretary of State, and Hoby was himself a first cousin of Robert Cecil, 1st Earl of Salisbury, who succeeded his father as the Queen's principal minister. As his mother pursued favours for herself and her friends, Hoby became a protégé of Burghley. Among his many other first cousins were the philosopher and statesman Francis Bacon and the spy Anthony Bacon.