For thirty-five years I have been researching and writing my family history. In the ancient teachings of the Gaels of Ireland is that one's ancestors assemble in the spirit world and choose from among their descendants one who will remember them. I am that one among my ancestors descendants who was chosen.
From this date on I shall post the various findings during my thirty-five years of family history research on the various histories of the O'Brien Clan. Today, the clan's surname around the world numbers about a half million people, this doesn't include the various derivations of the spelling of O'Brien. Not until the late nineteenth century did it become important to spell correctly. In fact about three hundred years ago in Europe, few people were able to write. The more numerous ways of spelling a word indicated one's better education. And about 1600 it became fashionable in England to replace the "i" with the letter "y," thus Brian became Bryan, etc.
The first name or Christian name of Brian is basically of unknown meaning. Researchers speculate on three meanings or origins to the word: 1) it may derive from the Gaelic word "bran" which means "raven." 2) It may mean "lofty" or "high place." 3) Last possible meaning is "great strength." But a Gaelic/Celtic origin word it is.
In ancient Gaelic/Irish the name was spelled Briain, and pronounced "Br-een." In some situations Briain is also spelled Bhriain (I think). The written "O'Brien" is strictly an English practice of the old Irish use of "Ua" and "Uí" before a surname. Actually the old Irish convention was quite accurate in its meaning; "Ua" is singular, and its use would be in identifying one of the name of Briain, i.e., Ua Briain. The spelling of "Uí" is plural which indicates all of the name Uí Briain. Modern Irish uses just "O" before a name. The change in spelling took place in 1543 when Murrough Ó Briain, last king of Thomond, surrendered his title to English King Henry VIII, and the spelling of "O'Brien" was created. Actually the meaning of "Ua" in Gaelic is translated to mean "grandson of," or "descendant of." The mac before a name in Gaelic means "son of." There is an old saying that mac spelled with an "a" has an origin in Scotland, and the mc indicates Ireland. Nice saying but no truth in it. Mac, Mc, M', all has the same meaning of "son of." In fact the use of the "O" is appropriate in Scotland too, but for some reason it just wasn't used except in a few instances. Therefore the surnames of O'Brien, O'Brian, O'Bryen, O'Bryan, O'Bryant, Brien, Brian, Bryan, Bryen, Bryon, Briant, Brient, Bryant, MacBrian, MacBrien, McBrian, McBrien, and Breen, are all variations in spelling of the name Ó Briain, which have their beginning with the founder or progenitor of the clan, Brian mac Cennédie "Boru," who lived from 941-1014 A.D.