Rees Ralph Llewellyn was born c. 1850 in Whitechapel. He matriculated to the University of London in 1869, where he obtained his medical degree in 1873. In 1874 he became a member of the Royal College of Surgeons, and in 1876 became a member of the Royal College of Physicians. He also became Medical Officer to E and EC Divisions, and City Mission
In the early hours of August 31st, 1888 he was called to Buck's Row where Mary Ann Nichols had been found murdered. He pronounced her dead, was briefly recalled to the morgue when more extensive mutilation was discovered, and the next day performed the postmortem investigation on the body. He testified as to the nature of her wounds at the inquest. He was not involved in the investigation of any further Jack the Ripper murders.
Llewellyn never married, and apparently lived with his siblings for his whole life. He died in 1921 at the age of 71.