Elongated Man and Green Arrow were two of the longer running JLA members who were featured in
Detective Comics who made the cover....
...but, there was one man who lasted even longer, but, because Batman always had the cover, had never had a cover of
Detective Comics while he was a back up feature in it.
Martian Manhunter
J'onn J'onnz premiered in
Detective Comics #225 (November, 1955) by
Joe Samachson and
Joe Certa, when Dr. Erdel accidentally beamed the Manhunter from Mars to Earth using his robot brain. The shock of J'onn's appearance was enough to send the doctor into cardiac arrest, killing the doctor and stranding J'onn on Earth. Being a manhunter on his world, he felt qualified to become a detective on Earth, and after taking the form of Earthman John Jones, he did.
The Martian Manhunter mostly hid his powers and alien nature for his earliest cases, he eventually did reveal his Martian form as a super-heroic identity in
Detective Comics #273 (November, 1959), joining the
Justice League of America soon after.
J'onn did have a few foes while running in
Detective Comics, like Monty Moran, the Human Flame and Professor Arnold Hugo (who, unlike the Martian Manhunter, made a cover of
Detective Comics,
#306, as he first faced Batman), as well as a few alien menaces, and even a new friend,
Zook. J'onn's Detective Comics run came to an end with
Detective Comics #326 (April, 1964), moving over to House of Mystery, where he finally got some covers.
The Martian Manhunter finally did make a
Detective Comics cover,
#715 (November, 1997), the second part of when he teamed up with Batman to face Firefly.
Aquaman
Aquaman was already a founding member of the JLA, and finishing a try out four issue run in
Showcase as he was losing his home as a back-up in
Adventure Comics that he had held for decades.
The Sea King and his young ally, Aqualad, got a temporary home with Batman and the Martian Manhunter, running from
Detective Comics #293 (July, 1961) to
Detective Comics #300 (February, 1962), after which, he started his own comic for the first time!
Sadly, Aquaman never made the cover of
Detective Comics, but the stories were drawn by
Nick Cardy, who also did the earlier issues of Aquaman's first series, and so, a representative cover of the era was chosen.
Elongated Man
When Martian Manhunter left the title, the book got a new back-up detective with the Stretchable Sleuth, Ralph Dibny and his wife Sue, starting with
Detective Comics #327 (May, 1964) by
Gardner Fox and
Carmine Infantino.
The Elongated Man moved over from working
with the Flash, and stayed in
Detective Comics, getting a couple of costume changes, working with Green Lantern, the Atom, Zatanna, Zatara, Commissioner Gordon...
...as well as a couple of full issues team ups with Batman and Robin, as well as facing foes like
Mirror Master, Chronos and the Riddler, until his continuous run ended with
Detective Comics #383 (January, 1969).
Elongated Man then made occasional appearances as a back-up feature in
Detective Comics (and was soon made a member of the Justice League of America as well at this time, which was a more regular home for him, as well as renewing his friendship with the Flash and his wife, Iris), usually with his wife, Sue helping him along.
The pair were traveling the country as Ralph used his Gingold powers to sniff out mysteries, including issues
#426, #430, #436, #444, #449, #453, #456, #457, #462, #465, #488 and
#500, as well as appearing with others in two issues that will come up!
Hawkman
Katar Hol, the Thanagarian policeman who was also a member of the Justice League of America, became an occasional back up feature in
Detective Comics starting with
Detective Comics #428 (October, 1972), after losing his own title, and even a title he shared with his friend, the Atom.
Hawkman (and eventually his wife, Hawkgirl), would appear in as back-ups once in a while, including in issues
#434, #446, #452, #454, #455, #467, #479, #480 and
#500 (as well as in one issue with Elongated Man and more...which more will be said on soon).
To be fair, Hawkgirl even made it into a
Roy Raymond feature in
Detective Comics #487 (December-January, 1979/1980, one of very few appearances of Hawkgirl without Hawkman) before the pair settled in
World's Finest Comics, which eventually led to the
Shadow War of the Hawkman, and then a regular comic series for Hawkman right around the time of the
Crisis On Infinite Earths.
Hawkman and Hawkgirl didn't make many covers, so instead, here's a few from
Brave and the Bold with Batman, including a foe introduced to Hawkman in
Detective Comics, the Fadeaway Man.
Atom
The Atom had also been a hero who lost his regular title, and was only appearing in the
Justice League of America, but he started up again as a back-up in
Action Comics for a while, but first he popped up with his fiancee, Jean Loring and friend, Alpheus Hyatt, for
Detective Comics #432 (February, 1973).
The Atom then kicked off a run of back-ups, with the Calculator as the focus with
Detective Comics #463 (September, 1976). Atom defeated him, but then appeared in the Black Canary back up of the next issue, and, along with all the heroes he faced in back ups (including Elongated Man, Green Arrow and Hawkman) in issues leading up to
Detective Comics #468 (March-April, 1977)...
...where Batman was finally able to beat the
Calculator (Aquaman appeared briefly here as well, as did the head of Metropolis' WGBS, Morgan Edge), which can be seen on this
Jim Aparo cover.
Atom also had one last back-up in
Detective Comics, facing a foe from the JLA, the Dharlu, in
Detective Comics #489 (April, 1980) before settling back in
Action Comics (alternating with the second Air Wave and Aquaman, including another battle with the Calculator), then getting into the
Sword of the Atom mini-series and specials around the time of the
Crisis On Infinite Earths.
Black Canary
Black Canary did have a brief time in
Detective Comics with
Detective Comics #464 and
#468 in the 1970s, but the majority of her appearances in the title were as a part of the Green Arrow back-up features, coming from the feature they shared in
World's Finest Comics, though Black Canary didn't show up until
Detective Comics #549 (April, 1985), eventually getting her new costume (as she dealt with changes in her life), and faced a foe based on a foe her mother faced, Bonfire.
Green Arrow and Black Canary also faced Steelclaw in Star City (and a team-up with Batman and
Catwoman), as their time in
Detective Comics wore down, ending
Detective Comics #567 (October, 1986), after which, she became part of the Justice League and Justice League International.
Green Arrow
Green Arrow had been a back-up in Action Comics and World's Finest Comics (mostly with Black Canary, and one back-up in
Detective Comics #466 with Elongated Man and with the group in
#468 facing the Calculator), but when he moved over to
Detective Comics with
#521 (December, 1982) under a
Jim Aparo cover.
Green Arrow spent most of his time concentrating on being a columnist for the Daily Star.
Green Arrow got some odd villains at this time based on simple gimmicks, like Hi-Tek, the Executrix, Ozone, the Detonator, the Printer's Devil, the Death-Dealer, Bad Penny, the Pinball Wizard, and Vengeance...
...before re-teaming with Black Canary, helping her with her history, and facing villains Champion, Steelclaw and Barricade, as well as working with Onyx, who came from the monastery Ollie had once taking refuge in (helping her out, and the mysterious Onyx stick around for a bit), as well as teaming with Batman and Catwoman for one full issue story...
....all before his back-ups ended with
Detective Comics #567 (October, 1986), and Green Arrow would then get a new look and attitude with
Green Arrow: The Longbow Hunters by
Mike Grell.
Red Tornado
Last, but not least, for JLA member
Detective Comics back-ups, it's worth mentioning that the android Red Tornado, while only really having a few back-ups in
World's Finest Comics, did come around to appear in a back up in
Detective Comics #493 (August, 1980) in a tale of Gotham City by
J. M. DeMatteis, Jose Delbo and
Joe Giella, with Reddy facing drug dealers, all under a
Jim Aparo cover...
...which also features back-up characters Human Target, which has already been covered, and Batgirl and Robin....who will be!