Thi is quite a toughie. I googled 'Famous Irishman' in Google images and this is the first answer I got!
A lucky shamrock to the first person to identify said Irishman. Clues may ensue.....
I would not have got him however many clues you does give us 
James Joyce?
If that is a portrait by American artist Thomas Nast....I bet I know who the subject is. But then maybe not, because I would have called the man an American? Hmm. Shall wait for clues.
I would have called him an American too, especially as he coined a phrase about the direction of the expansion of American territory and influence.
Well, I'm coming through the back doorway on this one. I'm a huge fan of Thomas Nast's art, and I could have sworn this portrait is one of his. But try as I might, I cannot confirm it through any of my sources.
I did an American History research paper on Thomas Nast for an upper division course at the University of Texas, decades ago. Many of my best source books were in the main library stacks, and "building use only". By now, they've all been sold, I bet.
Anywhoozle, this portrait is of Johnny O'Sullivan of "manifest destiny" fame. That was a silly struggle, since Texas didn't want to join the Union, and the Union didn't want Texas. Which, by the bye, Texas is the only state which has retained the right to secede. Driving through the Lone Star State, you may notice cars sporting bumper stickers demanding "SECEDE!", and these are entirely legal and appropriate sentiments, albeit futile.
If Texas succeeded in secession, I might well move there, heh. Though I'd surely miss Virginny.
Gosh! oh dear! That's all a bit Irish isn't it 
Was he Irish or not?
Here is the page I got him from Famous Irishman
Now tell me, who deserves the major shamrock? Asy, Midge? both? and Helio for a brave good guess?
I didn't know who he was - Auntie R told me, so I don't get the shamrock.
Well, I thought he was "that manifest destiny fellow that Nast drew", and had to google his name, so no shamrock for me either! [and I may be totally off about Nast as well...]
I think Merry should get the shamrock, for posing such an interesting question.
Seconded, wergh.
Though it may have been Nast because the piccy of O'Sullivan was on a cover of Harper's Weekly wot Nast did a lot of drawings and cartoons for.
Next Page...