[1] The son of Nicholas Underhill, a clothworker, he was born in St. Andrew's parish, Holborn, London, on 17 March 1634, and was admitted to Merchant Taylors' School in January 1645.
[1] The first character to which Underhill's name appears is Sir Morglay Thwack in D'Avenant's comedy The Wits, revived, with alterations, at Lincoln's Inn Fields on 15 August 1661.
[3] On the opening in 1671 of the new theatre in Dorset Gardens, Underhill was the original Sir Simon Softhead in Edward Ravenscroft's Citizen turned Gentleman (based on Monsieur de Pourceaugnac).
His liberty was demanded in April by Sir Allen Apsley, on the ground that he was one of the Duke of York's menial servants; the gaolers delayed until the case went to the House of Lords.
[5] After the two major acting companies were combined, Underhill came out on 4 December 1682 at the Theatre Royal as Curate Eustace in the production of Dryden's Duke of Guise.
On 6 February 1685, while Sir Courtly Nice was being rehearsed, Underhill had to inform the author, John Crowne, of the death of Charles II, by whose command the comedy had been written.
[1][6] An anonymous comedy, Win her and take her, or Old Fools will be Meddling,’ 1691, acted at the Theatre Royal the same year, was dedicated by Underhill to Lord Danby.
[1] On 5 December 1706 Underhill played at the Haymarket Theatre Sir Joslin Jolley in a revival of She Would If She Could by George Etherege, a part in which in the following month he was replaced by William Bullock; and on 20 January 1707 he repeated Blunt in The Rover.
The Mourning Bride (Congreve) was given for his benefit on 28 May; and on 3 June 1709 a performance of Hamlet at Drury Lane, where he played once more the first Gravedigger, repeated on 23 February 1710.