J'onn J'onzz, aka DC's Martian Manhunter, is an impressive, powerful, tier-1 character. He has been a part of DC canon for over 65 years, with his first appearance coming in 1955.
Depending on the story, he has been living amongst humans for years after initially coming here as a fully grown, centuries old Martian adult.
J'onn's powers and history are notable, being seen on a similar strength (if not speed and durability) level as Superman, along with having greater mental powers, shape-shifting, and similarly enhanced senses. While similar in the whole "ultra powerful, last survivor of their planet" role, Jonn is also far older, with backstory elements reaching centuries. They have often been shown having a strong kinship and understanding comradery.
The Manhunter was actually a part of the original Justice League of America comics....
He's even featured in the very first JLA story, seen here...
The character has had some notable development; while his initial secret identity was a Caucasian police officer, he has been notably played primarily----over the last 20 years especially---- by actors of color, both in voice work, and in physical roles. These portrayals were so recognized, they basically caused a bit of a "Ret-con," and now his human form of Detective Jon Jones (or rarely used other identities) is largely seen as having always been Afro American, a form J'onn takes on by choice...
That added diversity is one of the reason's the Manhunter was used as a "Founding member" of DCAU's 2000s Justice League series from the cartoon's start until it's end.
Oddly enough, though, the character never appeared in ANY of the earlier cartoon incarnations of the Super Team! To my memory, The Martian Manhunter was absent in most versions, from the 1967 "Cross over" toon....
to the 1973s Hanna-Barbera "Super Friends" version....
To Challenge of the Superfriends..
To when they moved solidly into the 1980s New Superfriends . This is notable because this was a period when they were adding entirely new heroes from different cultures to the team, some made specifically for the show itself...
To it's last Galactic Guardians intro...
By this point, however, Martian Manhunter had been a founding member of the League for over 25 years.
So, main question: Is there any official reason why Jonn Jones was never featured, or even mentioned in these older cartoons?
Did DC just not know how to use him, or was there some kind of issue to let Hanna-Barbera animate the character?
Was he simply not well known enough to be featured, and if so...why was that? Characters like El Dorado, Apache Chief and the Wonder Twins were completely new creations, so inserting an existing character with incredible powers (especially the mind reading and shape shifting) should have been easy enough...
Was there ever any "official" reason why this never occurred?