Henry Jermyn was an English nobleman born in 1605, known for his role as a courtier and politician during the reign of King Charles I. He was a prominent figure in the early 17th century and played a significant part in the royalist cause during the English Civil War. Jermyn is also recognized for his contributions to the development of St. James's in London. He was instrumental in the establishment of St. James's Square and the surrounding area, which became a fashionable district. His influence helped shape the urban landscape of London during that period.