Griphook is a goblin that worked at Gringotts Wizarding Bank in Diagon Alley. He later went on the run after The Fall of the Ministry and attempted to help Harry in search for another horcrux, hidden in the Lestrange Vault at Gringotts.
Griphook is a Goblin who sometime before 1991, took up a job at Gringotts Wizarding Bank in Diagon Alley.
 Philosopher's Stone
Griphook is first seen on Harry Potter's first trip to Gringotts to collect money from his parent's vault. Along with Rubeus Hagrid, he took Harry Potter to the vault 687 where Harry could collect some of his parent's money. He also brings the pair to Vault 713, where Hagrid collected the Philosopher's Stone for Albus Dumbledore. 
 Deathly Hallows
In 1997, while Lord Voldemort took over the Ministry, Gringotts bank was being overun by wizards, whom Griphook did not respect. Griphook eventually decided to go on the run and he met up with Dirk Cresswell, Dean Thomas, Ted Tonks and Gornuk. The group were eventually caught after spending several months hiding from the snatchers. When caught, Dirk, Ted and Gornuk were killed buy they took Dean and Griphook as prisoners in Malfoy Manor. Harry Potter, Ron Weasley and Hermione Granger were also later taken capture and brought to the manor, where they later escaped with Griphook and the other prisoners with the help of Dobby the house elf, to Shell Cottage. While his legs recovered from the Skele-Gro given to him by Fleur Delacour, he watched in respect as they group farewelled Dobby (who died in the aftermath of the escape) especially respecting Hermione.  The trio then asked Griphook to help them break into Gringotts to retrieve another horcrux they suspected that was in the Lestrange vault. He agreed but only if they gave him the sword of Godric Gryffindor. He helped them break in and they suceeded in retrieving Helga Hufflepuff's cup but later fled with the sword, alerting the other goblins of the break in. 
Being a goblin, Griphook is generally untrustworthy and sneaky who usually distrusts witches and wizards in count of the history they share.