D.J. (David Jacob) Connor, son of Roseanne and Dan.
D.J. (Donna Joe) Tanner, daughter of Danny, niece to Jesse and Joey.
Ren J. Hoek and Stimpson J. Cat
Damn you RawkStah, I was getting excited that no one else mentioned those two and that I can impress the board with my cunning intelluctual prowress.
Curses! Foiled again!
I thought it was all in homage to Michael J. Fox.
Since I don’t watch that much TV I despaired of thinking of anyone. Then I remembered:
CJ Craig of The West Wing.
I remember reading somewhere that there is a well-known, though yet unproven theory that every cartoon character has “J.” as a middle initial. On a completely unrelated note, some friends and I once noted that the middle name Elizabeth fits well with practically any name. Jane Elizabeth Smith. Maria Elizabeth Johnson. Adolf Elizabeth Hitler. (Nobody got the reference, did they?)
-Tyler J. (seriously, it is…)
Donald J. Trump
No disrespect, just an observation.
Jar J. Binks
I believe in some past thread it was established that “J.” is indeed a very common middle initial for American men. “John,” “Joseph,” and “James” would represent the bulk of those. But there are several other very popular “J” names—Jeffrey, Jason, Jordan, Jeremy, Jay, Jerome, Jonathan, Joshua, …
Earl J. Waggedorn.
I assume this is somewhat of a consequence that plenty of real people have J as their middle initial, which in turn is because an atypically large number of popular names start with J compared, at least compared to how many words in general start with J.
Not a fictional character, though. 
Yeah, I don’t think it needs any more explanation than that “J” is a very common initial.
Oh, and Mario’s middle name is apparently “Jumpman” (his first and last names, of course, are both “Mario”).
Is that kind of exactly what I said?
Technically B. J. Hunnicut, I suppose.
You’re about 17 years too late
Heh. I did a search for “hunnicut” to see if anyone had used it, It didn’t occur to me that some might have done so and misspelled it.
Yes. I swear it wasn’t there when I posted mine. It took a long time for the monkeys to retype it and deliver it to Chicago apparently.
No worries! 
Weren’t they all animated by Gamma Studios? 