Éirinn (agus Mheicsiceo) go Brách!
Despite the valiant efforts of those who would turn everyone Irish, Alvaro Obregón was not an O’Bryan… It’s a story that pops up now and again, though
Not Irish... sorry.
I’m not sure of the source (and presume it has a lot to do with the Irish propensity to make everyone Irish… at least on Saint Patrick’s Day… and the racial assumptions in the U.S. during the mid 1910s that wanted to deny the possibility that a mere Mexican was probably a better military officer without formal training than anyone in their own army at the time… and an inventor and political genius as well). There’s no harm in the stories, but I’ve had to correct it at least once in Wikipedia, and usually just sent a note to others who picked up the tale, pointing out that there are a number of prominent Obregón’s in the Spanish-speaking world (Alejandro, the Spanish-Colombian artist; Ana, the Spanish TV star; Diego, the Colombian pop singer; and Nancy, the Peruvian politician). Not to mention that Obregón is a town in Cantabria. The only oddity about Obregón as a name is that it’s Basque and easy to spell.
Kiss me, I'm Irish... honest!
Still, there are any number of good Irishmen and women, from the San Patricios to … Sor Juana (Juana Inés María del Carmen Martinéz de Zaragoza Gaxiola de Asbaje y Ramirez de Santilla Odonoju), to the O’Gormans (Juan, the painter and architect; and Edmundo, the historian and philospher) to the pre-mature independence leader William Lamport, a 17th century adventurer plotting the overthrow of Spanish colonial rule in Mexican 150 years too early and morphed in early 20th century pop culture into Zorro (really!!) … who have made their mark on Mexican culture….
Today we celebrate those, and the children of those who, having left their agrarian Catholic homeland famed for tenors, lightweight boxers and holding resentments against the English-speaking Protestants who occupied a third of the country, contributed to this agrarian Catholic land, famed for tenors, lightweight boxers and holding resentments against English-speaking Protestants who occupied a third of the country.
We make beautiful music together…
The Mex Files 
I’ve seen this story cited as the reason for making Obregon Irish:
“The Kansas City Star” (Missouri) Wednesday, July 19, 1916
NOT OBREGON —- O’BRIEN
Ninety-five years ago an Irishman was sent by the King
of Spain to rule as viceroy over Mexico. His name was
John O’DONAHUE — or Juan O’DONOJU in Spanish. His
closest friend and constant bodyguard was one Micky
O’BRIEN, re-named by his adopted Iberian brothers Miguel
OBREGON, and it was to him that Juan O’DONOJU turned
when Iturbide and his army, flying the banner of the “first
empire,” declared the end of the 300-year rule of the
Mexican viceroys.
Up the mountain wall from Vera Cruz went these two sons
of Ireland to where Cordoba clings like a swallow’s nest to
the seaward side of the sierra. And there Jack O’DONAHUE
and Micky O’BRIEN agreed to repudiate their emperor, and
allow Iturbide, the Morelian Indian, to rule until a king of
Mexico could be chosen.
And so well did Micky serve the first empire that he became
Gen. Miguel OBREGON, and was placed in control of the
western coast of the land of Mowuahtesuma, where, with his
wife who came from the land of his fathers, he left sons to lay
him to rest when his last day came.
A few weeks ago a stubborn president of Mexico, almost at
the end of his rope, sent a great-grandson of that same Micky
O’BRIEN (Alvaron OBREGON) to the rim of his country, bearing
arrogant demands, ungrantable requests, but with an army of
some 40,000 troops supposedly to back up those demands if
it came to blows.
OBREGON is more a master of his country today than anyone
has been since the time of Porfirio Diaz. From a small
hacendado he has become minister of war, an honor forced
from Carranza practically at the muzzle of an automatic pistol.
From head of a band of Yaqui Indians he has risen to command
an army of 150,000, probably the best army Latin-American has
ever known, and from an underling in the Madero and Carranza
armies he has raised his voice to dictate the policies of his
government and define what a marionette chief shall or shall not
do in his relations with foreign powers.
He demanded that Carranza keep his all but impossible promise
and give the people of Sinaloa lands for farming, and saw to it that
Carranza made good. He married Maria TAPIA, the belle of
Sonora, and carried her to the American border after his father-in-
law had put him out of the TAPIA home. When his bride told him
he should be minister of war, he traveled 1,300 miles to Mexico
City to secure the appointment.
Just as likely this putative Miguel Obregón is the ancestor of the Costa Rican Secretary of Education in the 1920s (for whom that nation’s national library is named), the Venezuelan real estate mogul or the Buenos Aires hairdresser who all revel in the name of Miguel Obregón.