O’Brien is born in Kinsale, County Cork. His real name was Patrick Cotter and he adopts O’Brien as his stage name in the sideshow circus, claiming descent from the legendarily gigantic Brian Boru. He is also known as the Bristol Giant and the Irish Giant. Another giant of this period, Charles Byrne, also claims to be an O’Brien.
It is believed that O’Brien dies from the effects of the disease gigantism.
No hearse can be found to accommodate his nine foot four inch coffin encased in lead, and his remains are borne to the grave by relays of fourteen men. In his will, Cotter leaves £2,000 to his mother and requests that his body be entombed within twelve feet of solid rock in order to prevent exhumation for scientific or medical research.
O’Brien’s remains are exhumed three times – in 1906, 1972 and finally in 1986. In 1972 O’Brien’s remains are examined and it is determined that, while alive, he stood approximately 8 feet 1 inch (246 cm) tall. This makes him the tallest person ever at that time, a record that is surpassed by the next “eight-footer,” John Rogan, who dies almost a century later. O’Brien is subsequently reburied but in 1986, during a redevelopment in the area, his remains are again identified and then cremated after a church service. O’Brien’s giant boots are on display in the Kinsale Museum.