The giant man-monster who lives in the sewers of Metropolis.
Solomon Grundy, named for the children's rhyme because he was "born on Monday," is a creature composed of Metropolis sewage that has reacted with refracted sunlight. Grundy is possessed of limited intelligence but immense physical strength and endurance. He is said to be "not real life--only a strange distortion of it" (S No. 301, Jul 1976: "Solomon Grundy Wins on Monday"). He is "only a strange imitation of a living organism" (S No. 320, Feb 1978: "The Absolute Power Play of the Parasite!").
Superman has encountered two beings who call themselves Solomon Grundy and share very similar characteristics.
In July 1976, Superman encounters the Solomon Grundy of Earth-2 who breaks through the dimensional barrier separating the Parallel-Worlds and materializes in Metropolis, bringing with him an infestation of swamp water. Following Superman's encounter with Grundy, which results in Grundy being stranded on the Moon, "the Slaughter Swamp Blight" peters out, leaving "enough slop behind to keep the sanitation department working overtime for a month," forcing Grundy's swamp water into the Metropolis sewers (S No. 301: "Solomon Grundy Wins on Monday").
Some months later the Parasite uses his Power Prism to refract sunlight into the sewers of Metropolis, creating a new Solomon Grundy from the waters of the original. Using his Prism to strengthen Grundy, the Parasite turns the monster loose on Metropolis, where he soon runs afoul of Superman. Convinced that he must capture Superman's cape to be his equal, Grundy engages Superman in a series of battles until the Man of Steel eventually succeeds in wedging Grundy between two cable-cars on the Sullivan Elevated Tramway high above the city (S No. 319, Jan 1978: "How to Make a Marshland Monster!"; S No. 320, Feb 1978: "The Absolute Power Play of the Parasite!").
In April 1979, Superman teams up with Swamp Thing to battle Grundy again. An attempt by Swamp Thing to experiment on Grundy results in the creation of sixty more duplicates of Grundy which are finally destroyed with a poison provided by S.T.A.R. Labs (DCCP No. 8: "The Sixty Deaths of Solomon Grundy!").
In appearance, Solomon Grundy stands well over seven feet tall, with chalky white skin and long white scraggly hair. He has fanged teeth and deep-set eyes. Grundy wears large brown boots and a torn black men's suit, several sizes too small.