In "After Twenty Years" by O. Henry, what is the character named Bob?

O. Henry's touching short story with the mildly surprising
ending is about two old friends, twenty years, and life's vagaries and changes. Bob and
Jimmy Wells at the ages of eighteen and twenty were set to go off on their separate ways
to make their fortunes and find their destinies. They agree to meet back together in
twenty years from the date and time of their parting to see each other again. A survey
of the movement of the story will help sort out what Bob
is.

Both are New York boys, Bob has an ambition to meet his
destiny and make his fortune in the West while Jimmy desires to remain firmly rooted in
New York City. As Bob tells the city policeman patrolling the street where Bob and Jimmy
are to meet, Bob moved around the West quite a bit and the two friends eventually quit
corresponding over the years:

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the West is a pretty big proposition, and I kept
hustling around over it pretty
lively.

Bob also says he
knows that if Jimmy is still alive, he will show up at the appointed place and confirms
that he will wait if Jimmy is late in coming. When a tall man huddled in an overcoat
approaches, he and Bob are reunited and start to walk "around to a place" for a
meal.

In the light of a drug store window, Bob sees that
the man isn't really Jimmy. Here is where we discover--if we weren't suspicious of it
already because of all the mentions of the West and all the diamonds sparkling on Bob
and his possessions--that Bob is a criminal from Chicago who is wanted by the Chicago
police. Jimmy turns out to be an impostor come to arrest
him.

The association of great wealth, criminal activity,
historical time period (c. 1904), and the city of Chicago lead the reader (especially in
O. Henry's day because it was a contemporaneous time period) to understand that Bob is
part of the Chicago gangster scene, reminiscent of the slightly later Al Capone. Jimmy
Wells, of course, was the patrol officer with whom Bob spoke, as his note
explains:

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"Bob: I was at the appointed place on time. When
you struck the match to light your cigar I saw it was the face of the man wanted in
Chicago. Somehow I couldn't do it [arrest you] myself, so I went around and got a plain
clothes [police] man to do the job.
JIMMY.”