Groot descends from a race of walking flora and resembles a sentient tree. Despite his adorably strange appearance and limited communication skills, Groot proves to be a valuable ally and a loyal friend -- not only to his fellow bounty hunter Rocket but to the rest of the Guardians of the Galaxy as well. He is also sweet, naive and a bit dumb, making him a very irresistible character.
After trying unsuccessfully to capture Star-Lord, the duo went to jail with Gamora and Star-Lord. Immediately alongside Gamora, Star-Lord and Drax make a plan to escape to Kyln, without notice Groot initiates the escape. The group starts a battle with the guards in which they are victorious.
During the meeting with the Collector, the Collector was very interested in Groot, and asked that after his death he could study his body, to which Groot agreed. Groot was responsible for saving Drax, who was beaten by Ronan.
During the Battle on Xandar, the Dark Aster was badly damaged when Rocket crashed it with the Milano. Groot created a protective shield with his body. Rocket begged him not to do so, and Groot wiped a tear from Rocket's face and said, "We are Groot." After that, his body was destroyed by the explosion of Dark Aster.
After his sacrifice, Groot was reborn (as a sapling) and is seen dancing with the music "I Want You Back" by "The Jackson 5", freezing whenever Drax looked his way.
Groot remains a baby for most of the film, with Rocket constantly needing to keep an eye on him due to his infantile state of mind and small size. He mostly plays a comedic role in the film, though is able to aid Rocket and Yondu in escaping the clutches of Yondu's mutinous crew member Taserface upon their capture, albeit with much frustration and continuous reiterating to the distractible and misunderstanding Groot. Groot is also able to set off the bomb that kills Ego the Living Planet, and in a post-credits scene, is shown to have grown to a teenage size and state of mind. This is the state he will appear in in Avengers: Infinity War.
Groot appears along with the rest of the Guardians in "Michael Korvac" searching for the cosmic fugitive Korvac. This version is very large, nearly the size of a tree, and shows the ability to regenerate himself at will.
Groot is an sentient alien plant who spends most of his time within a pot of soil. He appears to have a limited vocabulary, but his team mates can understand him. He can grow into a giant humanoid tree like being with superhuman strength. He is a leading member of the Guardians of the Galaxy alongside Star-Lord, Drax the Destroyer, Rocket Raccoon, Gamora, and Nova.
The Guardians battle the Chitauri, an alien race led by Korvac. When Rocket Raccoon's ship is pulled into the Chitauri ship, Rocket awkwardly fakes surrender so that they can free the captive Guardians of the Galaxy members. Afterwards, Spider-Man discovers that the Chitauri are planning to destroy the Earth. The Guardians plan to run the Chitauri ship into the sun while fighting the Chitauri forces. When their tactic does not work, the Guardians end up making their way towards the Dark Matter Cannon. While Nova and Spider-Man head to the Dark Matter Cannon, the Guardians fight the Chitauri and Korvac. After Korvac is defeated by Groot, Nova destroys the Dark Matter Cannon and the Chitauri ship is destroyed.
The adult version of Groot currently does meet-and-greets at Disney California Adventure, making his first appearance in Disney parks during Disney California Adventure's Summer of Heroes event. In addition, Groot appears in the Guardians of the Galaxy: Awesome Dance Off! street show before doing his meet-and-greets.