Fleming worked for DC Comics initially as a proofreader and later writer creating Thriller, and was writing an Aquaman limited series and one-shot special in 1989 with plotter/breakdown artist Keith Giffen and artist Curt Swan.
He is also known for co-writing (with Giffen) DC's popular comedic character, Ambush Bug in a handful of mini-series in the 80s. The duo have reunited for 2008's Year None.
"String-Out" (with Trevor Von Eeden, in House of Mystery #316, DC Comics, 1983)
Thriller #1-7 (with Trevor Von Eeden, DC Comics, 1983—1984)
Ambush Bug (with co-author and penciller Keith Giffen and inks by Bob Oksner, 4-issue mini-series, DC Comics, 1985)
Son of Ambush Bug (with co-author and penciller Keith Giffen and inks by Bob Oksner, 6-issue limited series, DC Comics, 1986)
Aquaman (with co-author Keith Giffen, pencils by Curt Swan and inks by Al Vey, 5-issue limited series, DC Comics, 1989)
Ragman (with co-author and penciller Keith Giffen and other pencils and inks by Pat Broderick, 8-issue limited series, DC Comics, 1991—1992)
The Darkness Within (with co-author Keith Giffen, pencils by Bart Sears and inks by Randy Elliott/Mark Pennington, 2-issue mini-series, DC Comics, 1992)
Eclipso #1-18 (with co-author and penciller Keith Giffen and various artists, DC Comics, 1992—1994)
"Tall Tale" (with co-author and penciller Keith Giffen and inks by Mike Allred, in Marvel Westerns: The Two-Gun Kid, one-shot, Marvel Comics, 2006)
Year None (with co-author Keith Giffen, DC Comics, 2008)