| Honorific-Prefix: | The Right Honourable |
| The Lord O'Brien of Lothbury | |
| Office: | Governor of the Bank of England |
| Term Start: | 1 July 1966 |
| Term End: | 30 June 1973 |
| Predecessor: | The Earl of Cromer |
| Successor: | Gordon Richardson |
| Birthname: | Leslie Kenneth O'Brien |
| Birth Date: | 8 February 1908 |
| Birth Place: | Dulwich, London |
| Death Place: | Redhill, Surrey, England |
| Restingplace: | Tandridge, Surrey, England |
| Nationality: | British |
| Occupation: | Banker |
Leslie Kenneth O'Brien, Baron O'Brien of Lothbury (8 February 1908 - 24 November 1995) was Governor of the Bank of England.
After attending Wandsworth Grammar School in London, he joined the Bank of England in 1927 and rose through the ranks, becoming chief cashier in 1955, deputy governor in 1966, before serving as governor from 1966 until 1973.[1] As governor, O'Brien presided over the devaluation of the pound in 1967.
He became a Knight Grand Cross of the Order of the British Empire in 1967 and was appointed to the Privy Council in 1970. Following his retirement as governor in 1973 he was created a life peer as Baron O'Brien of Lothbury, of the City of London.
He married firstly Isabelle Pickett (1908–1987) in 1932, and secondly Marjorie Taylor (born 1923) in 1989. He died in Tandridge, Surrey, in 1995.
| Crest: | In front of two Keys in saltire Azure a Needle point downwards proper threaded Gules |
| Coronet: | A Coronet of a Baron |
| Escutcheon: | Gules bezanty three lions passant guardant in pale each per pale Or and Argent |
| Supporters: | On either side a Lion guardant per fess Or and Argent in the mouth a Key Or standing upon a Heap of Coins Or and Argent |
| Motto: | Calm in Adversity |