Du Cros, William Harvey (1846–1918), entrepreneur, was born 19 June 1846, son of Edouard Pierre du Cros and Maria du Cros (née Molloy); the family was of huguenot ancestry, and lived in Moone, Co. Kildare, and Dublin. The young man was unhappy at home, especially after his mother died (1859), and after attending King's Hospital school (1855–60) equally unhappily, he left home to make his own way at the age of 15. He became a bookkeeper in Brooks Thomas, Dublin; married Annie Roy of Durrow, Queen's Co. (Laois), in 1866; and soon had the first of their seven sons to provide for. He became secretary of the Irish Commercial Travellers' Union in 1869, and owned a paperbag-making business. In his thirties he took up gymnastics, cycling, and other sports to improve his health. Always ambitious and competitive, he quickly made his name; he won Irish amateur fencing and light- and middleweight boxing championships, and founded and trained Bective Rangers rugby football club, which won the Irish championship with du Cros as captain. His sons were expected to join him in athletic pursuits, and his son Arthur du Cros (qv) became Irish cycling champion.
William H. du Cros, as president of the Irish Cyclists's Association, was approached in 1889 by two Dublin businessmen, William Bowden and J. M. Gillies, associates of John Dunlop (qv), who had developed the new air-filled tyre, then revolutionising the sport of cycling. Du Cros immediately seized his opportunity: a company was set up (1889) in which he had complete control, and those involved with Dunlop in earlier efforts to produce the new tyres were summarily dealt with. Production was moved to England after 1890, when Dublin corporation took action against the unpopular odours of rubber manufacture. The business under du Cros and his sons flourished: du Cros negotiated successfully with Dunlop and with others who patented improvements in rubber tyres and their manufacture, so that the company survived what could have been its downfall in 1890 when it was discovered that Dunlop's patent had not been novel, and was therefore invalid. The company (relying on the other patents it held, rather than on Dunlop's) expanded rapidly; Dunlop resigned from the board on 16 March 1895. In 1896 du Cros, backed by speculators, bought up shares in the Pneumatic Tyre Company and floated a new concern, the Dunlop Rubber Company. Du Cros oversaw the introduction of new products, including motorcar tyres from 1900, and helped introduce motor taxicabs to London; an attempt to do the same for Dublin failed, thanks to opposition from the jarveys. Du Cros was conservative MP for Hastings from the general election of 1906 till 1908, and was a chevalier of the Légion d'honneur. He moved back to Ireland in 1918, and died in Dalkey, Co. Dublin, on 21 December 1918. His first wife died in 1899; one of their sons had died in infancy. His second wife was Florence Gibbings of Devon.