Ó Maoláin is a Gaelic

Gaels

The Gaels or Goidels are speakers of one of the Goidelic Celtic languages: Irish, Scottish Gaelic, and Manx. Goidelic speech originated in Ireland and subsequently spread to western and northern Scotland and the Isle of Man....

-Irish

Irish people

The Irish people are an ethnic group who originate in Ireland, an island in northwestern Europe. Ireland has been populated for around 9,000 years , with the Irish people's earliest ancestors recorded having legends of being descended from groups such as the Nemedians, Fomorians, Fir Bolg, Tuatha...

 surname

Surname

A surname is a name added to a given name and is part of a personal name. In many cases, a surname is a family name. Many dictionaries define "surname" as a synonym of "family name"...

 usually anglicised as Mullin, Mullins, Mullan, Mallon, and Mellon, any of which may have an "'O'" prefix.

Overview

There are at least three unrelated families of the name native to Ulster

Ulster

Ulster is one of the four provinces of Ireland, located in the north of the island. In ancient Ireland, it was one of the fifths ruled by a "king of over-kings" . Following the Norman invasion of Ireland, the ancient kingdoms were shired into a number of counties for administrative and judicial...

, with at least one further family, again unrelated, found in Munster

Munster

Munster is one of the Provinces of Ireland situated in the south of Ireland. In Ancient Ireland, it was one of the fifths ruled by a "king of over-kings" . Following the Norman invasion of Ireland, the ancient kingdoms were shired into a number of counties for administrative and judicial purposes...

 in the County Cork

County Cork

County Cork is a county in Ireland. It is located in the South-West Region and is also part of the province of Munster. It is named after the city of Cork . Cork County Council is the local authority for the county...

-County Kerry

County Kerry

Kerry means the "people of Ciar" which was the name of the pre-Gaelic tribe who lived in part of the present county. The legendary founder of the tribe was Ciar, son of Fergus mac Róich. In Old Irish "Ciar" meant black or dark brown, and the word continues in use in modern Irish as an adjective...

 region. The Ulster Ó Maoláin's were as follows:

• Ó Maoláin of Ciannachta Glinne Geimin, a district of Tír Eoghain. Nowadays Mullin or Mullins.
• Ó Maoláin of Clones
  Clones
  Clones is a small town in western County Monaghan, in the 'border area' of the Republic of Ireland. The area is part of the Border Region, earmarked for economic development by the Irish Government due to its currently below-average economic situation...
  
  , County Monaghan
  County Monaghan
  County Monaghan is a county in Ireland. It is part of the Border Region and is also located in the province of Ulster. It is named after the town of Monaghan. Monaghan County Council is the local authority for the county...
  
  . Nowadays anglicised as Mullin or Mellon.
• Ó Mealláin, anglicised as Mallon
  Mallon
  Mallon is a surname that may refer to:*Andy Mallon, Irish Gaelic footballer*Bill Mallon*Brian Mallon*Dave Mallon*George Mallon*George H. Mallon , officer in the United States Army who received the Medal of Honor for his actions during the World War I.*Gui Mallon*Henry Neil Mallon*Jim Mallon*Mary...
  
  .