The often told tale was how Cyrus Gold mutated into Solomon Grundy after soaking for an untold period of time in the radioactive marshland outside Gotham City known as Slaughter Swamp. Like Alec Holland, former doctor turned sentient vegetation known as Swamp Thing, Grundy scared most whom he encountered. However, unlike the good Thing, Grundy was pure evil. After an initial confrontation which his future arch-enemy Green Lantern, which seemingly extinguished the pseudo-spark of life within him, Grundy was revived (and turned green) thanks to a concentrated shot of chlorophyll by a criminal Professor to serve as hired muscle. Instead, Grundy turned on his benefactor and unleashed a nationwide wave of terror unmatched previously. Finally dispatched once more by the Lantern named Alan Scott, rendered in stasis until a bolt of lightning reinvigorated him once more.
Again traveling across country, this time from the west back to the east to meet the Lantern for a rematch, he faced several members of the Justice Society. Seeming improbably, Grundy appeared in six cities wherein six Socialites battled him at the same time, one of which whom Johnny Thunder battled was a man disguised to look like Solomon. The others exhibited a "faster than light" replication which Grundy would display in his next appearance shortly thereafter, since their individual battles with Hawkman, Doctor Mid-Mite, the Atom, the Flash and Green Lantern occurred simultaneously.
After this third battle, Solomon was imprisoned by the Lantern on the moon, seemingly forever. Decades later, he returned from the moon to plague a new generation of heroes and travel to a parallel universe to spread his evil there! After seeing the Justice Society and their counterparts the Justice League together, Grundy wondered if he had a counterpart as well. And so, using his residual energy he had absorbed from the Green Lanterns whom he had just battled, Grundy journeyed to Earth-One to find his twin (who he already met in Blockbuster) and ended up battling that planet's Superman before returning to his home world. This laid the foundation for several clones of the monster, similar to his several incarnations on his home world throughout the decades.
However, before his return in the 1960's, Grundy had one final duel with his power ring protagonist. Note this truncated series of panels which presented a brand new Grundy to the world! On the left side of the panels, we see young Dick Cashmere, an astronomer separated from his father as a child somehow spying Grundy while the monster was on the moon. Through some techniques not revealed, Grundy seemingly flew back to Earth and then... here is the strange part... BECAME Dick Cashmere (or at least a duplicate of the lad). On the right side we see this fake Dick meet Alan and Doiby Dickles, at which point Alan suspects... due to the presence of a withered flower on Cashmere's person... that the young man was at the scene of a train disaster earlier. Tracking him down after noticing a picture of Dick Cashmere showing the face of Solomon Grundy, Green Lantern this time entombed him deep within the Earth (to be extracted by Per Degaton to be sent back in time to battle the All-Star Squadron). This Grundy reverted back to his previous Cyrus Gold disposition, the green version and Dick Cashmere version were apparently eliminated. Once more, Grundy was sent back to the moon and this time didn't regain the knowledge of anti-gravity and personality/appearance assimilation he had previously obtained.
On Earth-One, after the original Grundy's battle with Superman, some of his residue was left behind which Solomon had brought with him. And so, this unorthodox chemical composition was activated by the Power Prism of the Parasite to be used against the Man of Steel, although this new Grundy wasn't as malevolent as his "dad", and aided Superman against the villain. As a reward, Superman gave Grundy a cape and brought the man-monster to a world where he too could fly, and on this planet the beast would remain.
However, that wasn't the end of Grundy on Earth-One. Felix Faust changed a normal man into a Grundy and Swamp Thing copies, along with four others who impersonated fearsome foes to face the Super Friends, although he was eventually returned to normal after the conflict. Then, the remaining Slaughter Swamp sludge caused a chain reaction wherein other Grundy clones were spawned simultaneously in Metropolis. Eventually, Swamp Thing himself met one such clone of Grundy's, trying to ascertain if Solomon's biology could transform the Thing back into a human. Instead, the Swamp Thing discovered that each Grundy is a not definable as a life form yet still functions as such. Thanks to S.T.A.R. Laboratories, almost all the Grundys were destroyed. However, one remained that made his way to Gotham City, causing havoc there before Batman lured him into a furnace which consumed his inferior body (this case was the parallel to the first Grundy's encounter with Earth-Two's Huntress). Back over on Earth-Two, the original Grundy upon his returning in the middle 1960's to his home world from his decades long lunar exile empowered dozens of wooden objects with the same half life he himself had, and these entities sought to protect him from attacks lodged against him by Doctor Fate, Hourman and Lantern himself.
And so, the original Grundy's battle on Earth-One versus Superman mirrored that of Blockbuster of Earth-One fighting Superman in Earth-Two's Atlantis. The original Grundy based on Cyrus Gold from Earth-Two was the cosmic twin of Alec Olsen who became the first Swamp Thing of Earth-One. The counterpart to the Grundy Green Lantern that Solomon created on Earth-Two was Bizarro Yellow Lantern of Earth-One. The dozen Grundy clone whom Superman and Swamp Thing faced mirrored the animated wooden minions of Grundy whom Hourman and Doctor Fate had dealt with. The animated vegetation from Earth-Two's Slaughter Swamp mirrored Earth-One's Council of Trees.
The "Grundy" who battled the Super Friends and the "Grundy" who faced Johnny Thunder were dopplegangers, while the "Swamp Thing" that fought alongside him against the Super Friends was mirrored by green Grundy spawned by the Professor. And the first Grundy clone on Earth-One which Superman exiled to a another world to become a "caped crusader" was offset by the lightning spawned Grundy that battled the Justice Society back in the late 1940's before being exiled to the moon.
The enduring Solomon Grundy, the one who became a human twin of Dick Cashmere, found a counterpart in Alec Holland, the scientist who's mind transferred into vegetation that became what was known as the Swamp Thing.