The goblin who helps Harry and Ron break into Gringotts is Griphook. In Harry Potter and the Deathly Hallows, Griphook joins Harry, Ron and Hermione’s plan to infiltrate the wizarding bank and reach Bellatrix Lestrange’s vault.
Griphook is a Gringotts employee who first appears in Harry Potter and the Philosopher’s Stone, guiding Harry through the bank when Hagrid opens his vault. Years later, he is imprisoned at Malfoy Manor alongside other captives. Dobby helps free him, allowing Harry to recruit him for the dangerous break-in.
Griphook agrees to help in exchange for the Sword of Gryffindor, an object goblins regard as goblin-made property. His knowledge of Gringotts security, vaults and protective enchantments makes him essential to the plan. The trio disguises itself with Polyjuice Potion, while Griphook poses as a bank employee.
Readers sometimes confuse Griphook with Bogrod, another goblin involved in the vault sequence. Bogrod is compelled to assist them, but Griphook is the named goblin who plans and enables the break-in.