Why does a surname/family name begin O'

[cambelt2001]

I have noticed surnames/family names that start with O' then have another name like Connor / Sullivan etc.. Anyone know where this originates from?

[WaldoMcFroog]

Well, it denote 'of' and indicates a family name. 'O' means grandfather in gaelic. Nowadays names begining with O' almost always denote families of Catholic extraction.

[Octavius]

It is common for people of Gaelic origin to have surnames beginning with " �" , "Mc" or "Mac".

"O" was originally � (with a fada above the O) which in turn came from Ua (originally hUa), which means "grandson", or "descendant" of a named person as waldo ghas said.

The descendants of the High King of Ireland, Brian Boru were known as the Ua Brian (O'Brien) clan. The prefix is more likely to be written as O', using an English apostrophe instead of the Irish 'fada' mark.

[Fulton]

My wife's family name is Doherty. Generations ago, it was O'Doherty, but due to a run in with the law in Ireland, they were punished by having the O taken off them! Apparently this brought great shame on the family.
Can't see that working nowadays, kids would run out of letters!

[Senga 2]

I think AP is the Welsh equivalent of Mac, Mc and O as in Aprhys or Apthomas.

[almcd007]

My name is McDonnell and when I've looked into it , I've found it means son of Donnell where the Mc prefixes the name it's the same for O' and Mac etc