Thomas Underhill (1545–1591) served as Keeper of the Wardrobe of Kenilworth Castle and had charge of its contents after the castle was given by Queen Elizabeth I to her favourite Robert Dudley, 1st Earl of Leicester in 1563.
Thomas Underhill was born the son of Sir Hugh Underhill and one of Thomas Maynman's daughters in 1545 at Greenwich, then in the County of Kent. Maynman served as Keeper of the Wardrobe at East Greenwich, the location of the Palace of Placentia. Underhill would not only marry his daughter and have Thomas Underhill as a son, but he would go on to replace Maynman as Keeper of the Wardrobe in 1563.
Appointed by Robert Dudley Earl of Leicester, Thomas Underhill assumed responsibility as Keeper of the Wardrobe at Kenilworth Castle. Kenilworth was given by Queen Elizabeth to her favourite Robert Dudley, 1st Earl of Leicester. The fact that Thomas Underhill, son of a well-regarded member of her household was sent, shows the affection Queen Elizabeth I had both for Dudley and Underhill.
During his time at Kenilworth, Thomas Underhill would witness transformation of the castle by making the north entrance the main entrance to suit the tastes of Elizabeth, and adding the Leicester building, a large apartment, and a residential block overlooking the lake.
Elizabeth visited Dudley at Kenilworth Castle several times in 1566, 1568, and 1575. The last visit is especially remembered for Elizabeth brought an entourage of several hundred people who were entertained for 19 days at a reputed cost to Dudley of £1000 per day, an amount that almost bankrupted him.
Thomas Underhill and Magdalen Amyas married in 1570 and had one son, John Edward Underhill, who was born 1574 at Kenilworth.