What is the real identity of Mr. O Sullivan in 'The coming-out of Maggie' by O Henry?

You can find the answer to this question by reading to the
end of the story.  Just before the end of the story, we find out that "Terry O'Sullivan"
is really not an Irishman at all.  Instead, he is an Italian whose real name is Tony
Spinelli.

Maggie Toole has been unable all these years to
get a guy to like her and bring her to the dances.  So she has somehow managed to get
this Spinelli guy to come with her and has pretended he is Irish.  She only reveals what
is going on when she finds out that Spinelli is going to fight with Dempsey
Donovan.