Short answers, pulled from the story.
Pippin Took, full name Peregrin Took, is a fictional hobbit in J. R. R. Tolkien's The Lord of the Rings. He is the son and heir of Paladin Took II, Thain of the Shire, and one of four hobbits who join the quest to destroy the One Ring. He becomes a soldier of Gondor, fights at the Black Gate of Mordor, and later serves as Thain of the Shire himself.
Pippin's Westron name is Razanur Tuk. He is most commonly known as Pippin, a shortened form of his Sindarin name Peregrin.
Gandalf called Pippin a "fool of a Took" in the tunnels of Moria after Pippin dropped a stone into a deep hole. The noise appeared to wake something sleeping far below, which then signaled by tapping with a hammer, alerting enemies to the Company's presence.
Pippin took the palantir from the sleeping Gandalf without permission and looked into it, seeing Sauron himself. Sauron mistakenly assumed Pippin was the hobbit carrying the One Ring and that he was Saruman's prisoner. Gandalf then took Pippin to Minas Tirith to protect him from Sauron's forces.
When Denethor, Steward of Gondor, attempted to burn his son Faramir and himself alive in Rath Dinen, the street of tombs, Pippin ran to fetch Gandalf and the soldier Beregond. Their intervention saved Faramir's life, though it pulled Gandalf away from the Battle of the Pelennor Fields at a critical moment.
Billy Boyd played Pippin Took in Peter Jackson's Lord of the Rings film trilogy. Earlier adaptations featured Dominic Guard in Ralph Bakshi's 1978 animated film, Sonny Melendrez in the 1980 Rankin/Bass television film, and John McAndrew in the 1981 BBC radio serial.