Mr Denis O'Brien¹ was born in Caheragh, Drimoleague², Co Cork, Ireland on 9 March 1890.

He was the son of Michael O'Brien (b. circa 1851), a cobbler, and his wife Mary Hegarty (b. circa 1850), a domestic servant, who had married in Caheragh on 29 February 1876. 

As per the 1901 census, when he and his family were living in house 3, Caheragh, he had five known siblings: Bridget (b. 2 January 1877), Kate (b. 1880), Margaret (b. 12 November 1881), Michael (b. 29 May 1884) and Mary Ellen (b. 28 February 1886). 

His father apparently passed away sometime between then and the next census in 1911 but his final whereabouts remain uncertain; Denis and his widowed mother are recorded on the 1911 census living at house 20, Caheragh, the home of his married sister Kate O'Donovan and her family and he was described as a rural postman whilst his sister was listed as a "sub post-mistress."

Reportedly diminutive in stature, besides his postman duties Denis was also a gifted jockey, reportedly earning wins in his townland and further afield.

He boarded the Titanic at Queenstown as a third class passenger (ticket number 330979, which cost £7, 16s, 7d) and gave his local address as 196 Blarney Street, Cork. It is believed that his destination was the home of his sister Margaret in Manhattan.

Family lore tells that his brother Michael, also resident in New York, sent him a coat in which to travel in so that he did not look too destitute travelling through Ellis Island.

Denis O'Brien died in the disaster. His body, if recovered, has never been identified.