Gem, Thomas Henry (1819–1881), lawyer and tennis player, was born in Birmingham on 21 May 1819, the eldest son of William Henry Gem (d. 1856), a well-known Birmingham solicitor and one of the clerks to the Birmingham magistrates. He was educated under Dr Major at King's College, London, and articled at the age of sixteen to H. M. Griffiths, solicitor of Birmingham. On admission in 1841 he commenced practice in his native town. Though he built up an extensive private practice and acquired numerous legal and public appointments, ‘Harry’ Gem, as he was widely known, was principally known for his sporting, literary, and other public activities.

Gem was an active sportsman throughout his life, enjoying cricket, horse-riding, athletics, and ‘pedestrianism’, yet it was the game of lawn tennis for which he was known in the midlands. His part in the development of the rules of the game went largely unrecognized, save by his contemporaries in Birmingham and Leamington Spa. In the 1850s Gem was a keen racket player and leading spirit of the local club, but his enthusiasm was blunted by the necessity for expensively constructed courts. With his friend J. B. A. Perera, a Birmingham merchant, he drew up rules for a game named ‘pelota’ and later ‘lawn rackets’, with an emphasis placed upon simplicity and athleticism. The first game was played in the garden of Perera's Edgbaston residence about the year 1865. In 1872 Gem and Perera moved to Leamington Spa where they established a club and the name changed again to ‘lawn tennis’. Consequently, this predates the claims of Major Walter C. Wingfield to be the inventor of lawn tennis, the publication of his book on sphairistike, and the debate on the origin of the game in 1874–5.

In 1859, to the detriment of his other activities, Gem had thrown himself into the cause of the volunteer movement. He initiated the attempts to establish a local corps in Birmingham, holding the position of honorary secretary to the founding committee. At the time of his death Gem held the rank of major in the 1st Warwickshire (Birmingham) rifles. However, the movement made little progress in Birmingham and the waning of interest led to Gem's renewed preoccupation with tennis.

Gem was a prolific author. He wrote on numerous subjects and in a variety of forms, the majority of his works being for private or limited circulation. He contributed regularly to Baily's Magazine on a wide range of subjects, such as pugilism, horses, bull-baiting, and other sporting matters. Other material included election squibs (he was a staunch Conservative), songs, poems, verses (for example, on tennis), and a history of the Birmingham rifle corps. His major piece, completed shortly before his death, was a dramatization, in verse, of the Bardell v. Pickwick trial scenes from Charles Dickens's Pickwick Papers. In addition to writing for the stage, Gem was considered an accomplished performer of light comedy in local amateur productions. He was the first president of the Birmingham Dramatic Club and a member of the Birmingham Amateur Dramatic Association.

Gem also gained prominence locally as a result of his legal posts. On the death of his father in 1856 he succeeded to the office of clerk to the Birmingham magistrates. In addition, he held appointments as magistrate's clerk to the Kings Heath and Balsall Heath petty sessions and clerk to the commissioners of taxes for the hundred of Hemlingford.

In 1852 Gem married Ellen Maria Willcox (1831/2–1899). He died at 21 Portland Place, Leamington Priors, Warwickshire, from ‘paralysis’, on 4 November 1881.

Andrew Rowley