Comic book character, owned and published by Marvel Comics. He was created by Stan Lee and Jack Kirby, and made his debut in Tales to Astonish #13 in November 1960. Though his appearance was similar to the creature familiar to moviegoers, he was a much different character. In the late 1950s and early 1960s, Marvel specialized in comics about giant monsters threatening Earth, and that's what Groot was -- a tree monster from outer space kidnapping humans for study and experimentation. Though he was destroyed by termites in his first appearance, he was resurrected a few more times over the years to threaten the Earth. It was eventually revealed that the Groot monster who threatened Earthlings and the later heroic Groot were separate beings from the same species of interstellar plants.
At any rate, the Groot everyone knows and loves made his first appearance in 2007's "Annihilation: Conquest" crossover event, which was written by Dan Abnett and Andy Lanning. One of the very few survivors of the Flora colossus species of Planet X, Groot assisted Star-Lord and members of his cosmic strikeforce as they fought Ultron and the Phalanx. Rocket Raccoon was one of the few members of the strikeforce who could understand Groot's language, so they bonded unexpectedly well. Groot was actually destroyed several times during the storyarc, but always regrew, often very quickly, from very small twigs.
After the Annihilation crossover ended, Abnett and Lanning decided to make a new Guardians of the Galaxy team with their favorite characters from the crossover, including Star-Lord, Groot, Rocket, Drax the Destroyer, and Gamora. The ongoing series gave Abnett and Lanning lots of opportunities to expand on Groot's character and background. One of the fun bits they came up with was his inability to say anything other than "I am Groot!" Though most characters believed he was a simple-minded creature, it turns out that Groot's species was physically incapable of saying anything other than those three words, but he still managed to pack those few words with vast amounts of information, if you knew how to listen to him.
Groot's powers involve a number of plant-related abilities. He's able to regrow himself from the smallest cutting or twig, he's able to expand his height and mass tremendously, and he has very high strength and durability. He's also able to control plants and can absorb wood as food. Groot's people appear to be uncommonly intelligent, but Groot himself is a great deal smarter than the average, possessing genius-level skills in "quasi-dimensional super-positional engineering."
Groot has had several different origin stories. In the first, as a young sapling, he didn't get along well with the other treefolk on Planet X because he preferred the company of the downtrodden, squirrel-like "Maintenance Mammals" who kept things running. He killed another sapling that was attacking one of the Maintenance Mammals, and was exiled from his homeworld. A later origin claimed Groot's people were abducting creatures from other planets for experimentation (like the Groot monster in the original Stan Lee/Jack Kirby story). Deciding it was wrong to kidnap others, Groot returned an Earth girl back to her home and was cast from Planet X as punishment.
Groot appeared in the "Guardians of the Galaxy" film in 2014, its 2017 sequel, "Guardians of the Galaxy Vol. 2," 2018's "Avengers: Infinity War," and 2019's "Avengers: Endgame." He was voiced by Vin Diesel, who apparently took great delight in playing a role where he got to express himself solely by saying "I am Groot." Diesel also performed the voice work in multiple foreign languages as well, for the international film releases.