In Rick Riordan's Percy Jackson and the Lightning Thief, Grover wants a searcher's license so that he can take up a quest of his own: the search for Pan. This is a task that some of the most dedicated satyrs—the half-man, half-goat worshippers of the nature god, Pan—have taken up, but none of them have been successful, and many of them, including Grover's uncle, have never come back. Despite all of the risks involved, Grover feels called to this search and hopes that by taking it up and succeeding in finding Pan, he can finally redeem himself from the tragedy that he deems his biggest failure: the death of Thalia, a demigod whom he was supposed to protect and bring safely to Camp Half-Blood.

Percy Jackson and the Olympians: The Lightning Thief is a 2006 novel by Rick Riordan, the first book in his series of Percy Jackson novels. In the story, the gods and myths of ancient Greece exist in real life and are set in the contemporary world.

In Percy Jackson's world, a searcher's license is a special permit issued to satyrs (half men, half goats) that allows them to search for the nature of the deity Pan, god of the wild. Grover, meanwhile, is the best friend of Percy, the protagonist, and is of satyr stock, a fact that is alluded to early in the story when Percy says Grover has "some kind of muscular disease in his legs." Later, Percy learns that Grover is a "Keeper" whose job is to protect him (a mission at which he has failed). To redeem himself, Grover decides to find Pan, a quest that requires him to obtain a searcher's license.

After several setbacks, Grover ultimately obtains his searcher's license.

Why does Grover want a searcher's license in Percy Jackson and the Olympians: The Lightning Thief?  

Grover, or the "G-Man" is Percy's best friend in this series of books by Rick Riordan.  He's an unlikely hero, because in his "human" life, he's bullied and misunderstood, cries easily, is physically inept--actually, crippled might be a better word (except when the lunchroom is serving a meal he likes, at which time he ignores the muscular disease which makes mere walking painful, and gets into line rather quickly).  Grover is kind, perceptive, and a tree hugger of sorts, which is consistent with his heritage as a satyr.  Getting a "searcher's license" will be necessary if Grover wishes to search for Pan, the god of wild places, as he tries to redeem himself after failing to keep Percy safe, as required by his role as a Keeper.