Quick comparison of Man-Thing to Swamp Thing! Both of these characters are comic book superheroes created by different publishers, yet they share many similarities in appearance, abilities, and backstory.
In terms of appearance, both Man-Thing and Swamp Thing are monstrous, swamp-based beings composed of plant-life and muck. They both possess superhuman strength, regenerative abilities, and the ability to control plants. In terms of backstory, both characters started out as scientists, working in secret to develop formulas for enhancing human biology. Both are victims of espionage and betrayal, forced to flee into the swamps with their research, only to be killed and subsequently transmuted into monstrous swamp-beings.
However, there are some key differences between the two characters. Man-Thing is barely sentient and serves as the guardian of The Nexus of All Realities, while Swamp Thing is a plant elemental with the memories of human Alec Holland and is the emissary and defender of The Green. Swamp Thing has the ability to manipulate plant life, while Man-Thing does not. In addition, Swamp Thing is portrayed as a virtual god, while Man-Thing is portrayed as a healer and protector.