FOREVER PEOPLE (vol. 1) #1 (March, 1971). Cover by Jack Kirby.
The first appearance of Jack Kirby's idea of cosmic hippies - The Forever People.
Despite being released a few months after Kirby first started his Fourth World Saga in Superman's Pal, Jimmy Olsen (vol. 1) #133 (October, 1970), the events in this story actually occur before that issue. Guest-star Superman (billed as "the immortal Superman") learns of Darkseid, glimpses New Genesis for the first time (which The Forever People keep referring to as Supertown), and even gets his first ride in a Boom Tube.
But despite the introduction of more of his cosmic characters, it's Kirby's take on Superman in this issue that has stuck with me over the years.
Superman, as Clark Kent, interviews a champion boxer who reveals that he resents Superman. The champ, despite holding the title and being loved by the public, feels inferior because anything he can do Superman can do 100 times better.
That leads Clark to ruminate:
Poor Superman! Despite his powers, he is a minority of one in a teeming world of billions! A stranger in a strange land... What does Superman mean to you, down there? Do they secretly resent him? Fear him--? Hate him? For the first time in many years-- I feel I'm alone-- Alone!
However, Superman was NOT alone. Kirby seemed to forget, or conveniently ignored, the existence of: Supergirl, the bottle city of Kandor (inhabited by more Kryptonians, albeit teeny weeny ones), the Justice League, the Doom Patrol, the Teen Titans, and the many other super beings that inhabited Earth at the time.
Nevertheless, introducing the idea that people may not be fond of Superman - despite all the good he's done - simply because he exists and what he's capable of, was a good idea.
I think other writers later weaved that into the motivation for why Lex Luthor hates Superman, as opposed to the old motivation from the Silver Age that Luthor was mad Superboy made him bald.