Ó Cléirigh

O'Cleary or O'Clery (Ó Cléirigh) is the surname of a Gaelic Irish family. It is the oldest recorded surname in Europe — dating back to 916 AD — and is cognate with cleric and clerk. The O'Clearys are a sept of the Uí Fiachrach dynasty. As Connachta, the O'Cleary's ruled the kingdom of Uí Fiachrach Aidhne for nearly 800 years. They are the descendants of Fiachrae, son of the High King Eochaid Mugmedon, and elder brother of legendary High King Niall of the Nine Hostages. According to legend, they ultimately trace their ancestry back to the mythical Fir Bolg, as well as to Milesius, and consequently to Japheth, son of Noah.

During the Norman conquest of Ireland, they were expelled from their land and replaced by their cousins the O'Shaughnessy's. From the early 11th or 12th century, they were based in Tír Chonaill, located in modern-day County Donegal, where they served as poet-historians, scribes and secretaries to the O'Donnell dynasty of Tyrconnell. They authored the Ó Cléirigh Book of Genealogies. The clan Cleary and its branches also appeared in Scotland (sometimes known as McCleary), due to the historical connection and exchange between the two countries, much like the Campbells.

Naming conventions
The name has been Anglicised variously as O'Clery, Cleary, Clery, Clark, Clarke and Clarkson.

Ó Cléirigh

 * Mac Comhaltan Ua Cleirigh, King of Uí Fiachrach Aidhne, fl. 964
 * Lughaidh Ó Cléirigh (fl. 1595–1630)
 * Mícheál Ó Cléirigh (ca. 1590–1643), considered the chief author of the chronicle of medieval Irish history known as the Annals of the Four Masters
 * Cú Choigcríche Ó Cléirigh (died 1664)

O'Clery

 * Keyes O'Clery
 * Conor O'Clery

Cleary

 * Bernard Cleary (born 1937), Canadian politician
 * Beverly Cleary (1916–2021), American author
 * Bill Cleary (born 1934), American hockey player
 * Brendan Cleary (born 1958), Irish poet
 * Brian P. Cleary (born 1959), American humorist, poet and author
 * Daniel Cleary (born 1978), Canadian hockey player
 * Gabriel Cleary, Irish engineer
 * Ivan Cleary, rugby league footballer and coach
 * Joe Cleary (1918–2004), Irish baseball player
 * John Cleary (disambiguation), several people
 * Jon Cleary (born 1917), Australian author
 * Jon Cleary (musician) (born 1962), American musician
 * Mark Cleary (professor) (born 1954), Vice-Chancellor of the University of Bradford
 * Michael Cleary, several people
 * Nikki Cleary (born 1988), American singer
 * Paul Cleary (born 1976), Australian middle-distance runner
 * Phil Cleary (born 1952), Australian commentator
 * Patrick Roger Cleary, founder of Cleary University
 * Sean Cleary (footballer) (born 1983), Irish football player
 * Sean Cleary, Irish rugby league footballer
 * Thomas Cleary, American author and translator
 * William J. Cleary (1870–1952), American politician

Clarke

 * Austin Clarke (poet) (1896–1974), Irish poet
 * Henry Edward Clarke (1829–1892), businessman and politician in Ontario, Canada
 * Henry Joseph Clarke (1833–1889), Premier of Manitoba, Canada, 1874–1878
 * Peter Clarke (tennis) (born 1979), Irish tennis player
 * Philip Clarke (politician) (born 1933), Irish Republican Army member and politician
 * Tom Clarke (Irish republican) (1857–1916), executed for his part in the 1916 Rising

Other institutions

 * Cleary University, a private business school in Michigan, United States
 * Cleary Gottlieb Steen & Hamilton, an international law firm
 * The Clery Act of United States law
 * Clerys, an Irish department store