The DC universe is chock-full of gods. Some are old, some are new, but most of them are bullies with an extreme superiority complex and an itching need to occasionally wipe out anyone weaker just because (mostly that's Darkseid). Luckily, there are beings in the DC universe who can handle these bullies and even defeat them single-handedly.
Kryptonians, Amazons, anomalies of nature, heck, even human beings can sometimes become strong enough to teach the DC gods a lesson in humility. Here are some very powerful members of the DC universe who have beaten the best-known and most popular designated gods of DC.
Of course he'd be here, he's perhaps the strongest and most versatile (in terms of superpowers) superhero there is! Superman (Clark Kent/Kal El) is usually the only thing keeping his own universe intact and the most notable and persistent god he's defeated would be Darkseid. More than once in all of the comic books, cartoons, and movies, Superman has defeated Darkseid fair and square.
In one of their fights, Supes was even able to withstand Darkseid's Omega Beam, using only his heat vision. Usually though, it's Superman's raw solar-powered strength that always puts Darkseid (or his avatar) into submission.
The politics of the seven seas in the DC universe is quite complex and involves gods interacting with mortals. As such, when it was Aquaman's (Arthur Curry) turn to rule Atlantis, a certain son of Poseidon named Triton got a little too insecure and started throwing a tantrum against Aquaman.
Triton, being one of the Olympians and considered as a god, challenged Aquaman to one-on-one combat. Surprisingly, Triton's strength was dictated by how many worshippers he had and he was a bit on the low side when he fought Aquaman. This led Aquaman to win the fight and humiliating Triton so much that Poseidon even blinded Aquaman as punishment for beating his son down.
8 WONDER WOMAN
Another member of the Justice League who gets constant headaches involving Olympians is Wonder Woman (Diana Prince). Her sworn enemy is even Ares, the God of War and one of the most prominent gods of Greco-Roman mythology. Wonder Woman, nearly having the level of might of Superman herself, has occasionally dealt with Ares single-handedly.
One such victory against the God of War happened during one of Ares' orchestrated attacks against Themyscira, Diana's homeworld. An enraged Diana quickly stormed Ares' comfy perch, grabbed a battle axe and split his head open before he could boast of his recent military campaigns to the Amazon.
As a monster who managed to slay Superman at one point in single combat, Doomsday ought to have no problem defeating literal gods. Turns out, the most significant god he defeated was Darkseid. This took place in Rematch: Hunter/Prey where a supposed rematch between Doomsday and Superman has the former warming up first by sand-kicking Darkseid in the face.
No kidding. Somehow the writers of the said series made Darkseid a lot weaker than he should be, not that he needed the nerfing for Doomsday to beat him. In any case, Doomsday canonically has the honorary title of defeating a god of the DC universe.
Spectre is an almost unstoppable force, no matter who the being chooses to possess or assume. Not many things can defeat Spectre at all, for that matter.
So, when Spectre was manipulated to destroy magic, he looked to the wizard Shazam (the one who granted powers to Billy Batson). This happened in the Day of Vengeance storyline, where Spectre went on a nigh-unstoppable hunt for those with formidable magical powers. Shazam even prepared for a one-on-one fight against Spectre. Just when it appeared that he has won, Spectre managed to revive himself and deal a killing blow against Shazam. As it is, the wizard Shazam is also considered as a god in DC and he was bested by the right hand of another god.
5 BLACK RACER
Black Racer is the resident manifestation or physical aspect of Death itself in the DC universe. Darkseid even took a liking to Black Racer long ago and proceeded to imprison him as a weapon. Too bad that weapon backfired on him when both Flashes (Wally West & Barry Allen) led Black Racer to Darkseid with hopes that the former would lay waste to the latter.
Black Racer beat Darkseid to a pulp and nearly killed him but had to be stopped before things got out of control. Afterwards, the Justice League of America went in and finished the job Black Racer started.
Orion already has a promising future from the moment he was born. Being the son of Darkseid himself, Orion was prophesized to be the downfall of Darkseid sometime in the future. Hence, the two eventually turned on each other in a celestial fight to the death, during which Orion managed to rip out Darkseid's heart and kill him.
Orion even went on to become a New God of DC himself, though he's not exactly on the same level of omnipotence as his father. Nevertheless, Orion still managed to fulfill the prophecy tied to him and defeating Darkseid is no easy feat.
Zeus in the DC universe seems to mostly conform to his Greek mythology roots, meaning his origin may as well be the same. That is, Zeus single-handedly killed his own father, the Titan Cronus, and assumed his place as King of the Gods.
It's safe to say that Wonder Woman's father is certainly a powerful god who has defeated many of his fellow contemporaries single-handedly. At times, even a regular Superman was put in his place by the King of Olympians.
Batman has faced and injured Darkseid at one point, in one of his most impressive feats. Awesome as that may be, his nemesis, the Joker, has done something far more astonishing against Darkseid. The Joker, in a series called Emperor Joker, acquired Mr. Mxyzptlk's multiverse-bending powers and turned Darkseid into a joke.
Emperor Joker didn't even have to unleash pain against Darkseid. The Ruler of Apokolips immediately knew that he would be no match for the Clown-Prince-of-Crime-turned-Emperor and surrendered to him. It's one of the most embarrassing defeats Darkseid has had to endure.
Darkseid is quite similar to Zeus: he's a god and he has to humble other gods before they get too uppity. It just so happens that one of the many gods Darkseid has beaten or killed is also Zeus, along with the other Olympians-- it was basically an Mt. Olympus clearing operation.
In an Olympian-like fashion himself, Darkseid also killed his own father, another god, in order to assume his power and become the Ruler of Apokolips as well as the God of Tyranny. It's too bad Darkseid's karma got the best of him; there have been many in the DC universe who have already defeated him and his ilk. Oh well, what goes around comes around.