DC Comics has three beings of great power on their roster who have usually proven difficult to put into their larger continuity.
Captain Marvel, Martian Manhunter and The Spectre!
At various times, The Spectre (created in 1940) and Captain Marvel (1940) have been members of the Justice Society of America (1940), while Martian Manhunter (1955) has generally been a member of the Justice League of America (1960).
Captain Marvel and The Spectre were pivotal characters in DC's masterpiece KINGDOM COME (1996) by Mark Waid and Alex Ross, while Martian Manhunter figured prominently in JUSTICE (2005) by Ross, Jim Krueger and Doug Braithwaite.
But Captain Marvel works best under the umbrella of the Marvel Family (Captain Marvel Jr., Mary Marvel, Tawney the Talking Tiger, Mister Mind, et al).
Captain Marvel is a genre character, a trait he shares with many heroes created in the 1940s. Plastic Man was created by Jack Cole in 1941 and, like The Spirit (created by his old boss Will Eisner in 1940), works best in a self-effacing, isolated, slightly twisted slice of noir that runs contrary to the majority of the DCU.
Martian Manhunter is a stickier situation for all involved.
Created at the height of the bumper crop of pseudo-science heroes brought out by DC when super heroes were all but eliminated by the Wertham SEDUCTION OF THE INNOCENT Senate-driven blackout of the 1950s; along with Adam Strange (1958), Captain Comet (1951), and The Phantom Stranger (1952), Martian Manhunter had abilities approximate to Superman, but was vulnerable to fire, able to read minds, turn invisible and alter his physical appearance.
Martian Manhunter was used to great effect in Darwyn Cooke's THE NEW FRONTIER (2004), and of course was a founding member of The Justlce League of America, but has never had his own title for more than a year.
Why has Martian Manhunter been largely ignored by the public?
I argue that WITH GREAT POWER COMES GREAT ANTIPATHY from the audience!
Martian Manhunter is both TOO POWERFUL by half yet TOO EASILY DEFEATED by Zippo lighters to ever be a hero that audiences can look up to.
The Spectre is so powerful that it is only a question of HOW he's going to kill you, not IF he's going to kill you, and that trick gets old plenty quick.
Some heroes have too much going against them (genre, powers, the ability to play well with others) to ever enjoy sufficient "suspension of disbelief" and to generate a fervent fan following.
Martian Manhunter can read minds, which is less of a super power than it is a plotting device!
In Grant Morrison and Frank Quitely's brilliant JLA EARTH 2 (2000) graphic novel, Martian Manhunter quickly pegs Superwoman as a degenerate in sheep's clothing, which is valuable information to the reader.
During Morrison and Howard Porter's reboot of the JLA (2006), it is Martian Manhunter's awareness of who the "supposed Samaritans from outer space" really are that saves the day.
However, in a pure "whodunnit" like Brad Meltzer, Rags Morales and Michael Bair's classic IDENTITY CRISIS (2004), well, Martian Manhunter is nowhere to be found, because he could solve the central mystery instantly by using his telepathy!
Reading minds is great when used against the ENEMY, but is usually alienating and creepy when used against ALLIES. More times than not, Martian Manhunter is less embraced by his friends than he is avoided by his comrades.
Generally, Martian Manhunter is brought into the JLA title when the Trinity (Batman, Superman, Wonder Woman) are not available (due to broken backs, death by Doomsday or disintegration by a Crisis On Multiple Earths).
This means that Martian Manhunter is put in charge when the C-squad is populating the JLA; like former members of the Teen Titans, Mister Miracle or Booster Gold; and those adventures are primarily played for laughs.
For all of his power, Martian Manhunter is often just a joke, which makes it hard for him to be taken seriously as a hero!
The fact that he also tends to see himself as a victim; as in JLA: A MIDSUMMER'S NIGHTMARE (1996) by Mark Waid, Fabian Nicenza, Jeff Johnson and Darick Robinson; does not help his street cred, much!
If Martian Manhunter stops whining, smirks less and pulls up his Speedos a bit more, maybe he'd be a better fit in the DCU. Until then, he's just not ready for the big screen!