Around 1931, the giantess Fridwulfa abandoned her human husband, Mr. Hagrid, and her young son, Rubeus, a Half-giant, who was smaller in stature than she would have liked. She rejoined her own kind in the mountains, and there she found a mate in an unknown giant. She later gave birth to Grawp, who despite being a full-blooded giant, was still particularly small. As such, she abandoned her second son as well.
Hagrid kept Grawp in the Forbidden Forest for months, teaching him manners and bits of English. Grawp was rather violent over the course of the year: known at times to empty bird nests and let the eggs be destroyed, attempt to rip up the trees that he was tied to, as well as attack his brother Hagrid and attempt to grab Hermione Granger; however, in 1996, he became more docile. He later attended Dumbledore's funeral with Hagrid, where it appeared that he had at least some understanding of human emotion, since he patted his half-brother's head to comfort him, though unintentionally smashing him to the ground due to his immense strength.
Grawp hid with Hagrid after he escaped arrest for having a Support Harry Potter party in his hut. They hid in caves and mountains. Dumbledore's Army was founded again to rebel the Death Eaters rule of Hogwarts and the Ministry and to Protect students of Hogwarts from Snape and the Carrows.
When Harry Potter, Ron Weasley, and Hermione Granger returned to the Death Eater controlled Hogwarts. Grawp and Hagrid participated in the Battle of Hogwarts. As they could hear Voldemort's enhanced voice from their cave, they came to the battle as quickly as they could. Grawp lifted Hagrid into the castle, and fought against the other giants (who were on Voldemort's side, and it was remarked that compared to the other giants he was indeed very small.) They both ultimately survived the battle. He disappeared initially when the first part of the battle ended but returned to fight the other giants, this time with the help of Buckbeak and the Thestrals, and presumably defeated them. He surfaced from the battle alive, and it is said that the gatherers in the Great Hall threw food into his laughing mouth through a broken window.
Grawp was rather aggressive, which was a common trait for a giant, and was known to beat up Hagrid when in a bad mood. Hagrid claimed that he didn't know his own strength. Despite being aggressive at times Grawp loved his half brother and when Hagrid was forced to leave Hogwarts, Grawp searched for him and was upset when Hermione was unable to tell him where Hagrid was.
'Grawp' in English sounds more like a grunt than a name, a graphic demonstration of the limited vocal ability of the giants. Grawp himself has trouble pronouncing words of more than one syllable. He found it difficult to speak English and was unable to form full sentences. He also had a tendency to mispronounce peoples names, calling Hermione "Hermy" and Hagrid "Hagger". As he aged, however, Grawp grew less and less violent, and was described as "almost tame" while at Albus Dumbledore's funeral, patting Hagrid on the head in an attempt to comfort him, albeit smashing the chair Hagrid was sitting on in the process.
The original model for the film was created in 2004 by Gerald Gibbons who based it on a student he had taught back when he was a teacher. The student, Tom Hull, now attends the University of Bath.
The film adaptation shows Ron Weasley accompanying Harry and Hermione during their first visit to Grawp, as opposed to the book in which Ron was playing in a Quidditch match at that time.
It is possibly that his name is different from this as Hagrid said that it sounded like Grawp when he says his name.
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