The G-man. Percy's best and only friend in the world. Grover has stuck by Percy throughout sixth grade and has kept watch over him. Percy meets Grover at Yancy Academy and spends much of the time protecting him:
Grover was an easy target. He was scrawny. He cried when he got frustrated. He must've been held back several grades, because he was the only sixth grader with acne and the start of a wispy beard on his chin. On top of all that, he was crippled. He had a note excusing him from PE for the rest of his life because he had some kind of muscular disease in his legs. He walked funny, every step hurt him, but don't let that fool you. You should've seen him run when it was enchilada day in the cafeteria. (1.20)
This description tells us that Grover is similar to Percy in that he's "different" from the other kids at school, making him an outsider, just like Percy. He looks older than the other kids too, making us wonder whether he's a bit more emotionally mature than they are. And, lastly, he loves food – a fact that will constantly reveal itself over the course of Percy's story.
At Camp Half-Blood, Grover is very nervous around Mr. D. Why? Chiron gives us the scoop:
"Grover has big dreams. Perhaps bigger than are reasonable. To reach his goal, Grover must first demonstrate great courage by succeeding as a keeper, finding a camper and bringing him safely to Half-Blood Hill." (6.16)
According to the Council of Cloven Elders, Grover did not bring Percy safely back to Camp Half-Blood the night the Minotaur attacked – Percy brought him (literally, he carried an unconscious Grover onto camp property). And, in the Council's eyes, Grover also failed to bring Thalia to safety so many summers ago (an event that broke Grover's heart and that weighs on him still). That means that, technically, Grover has failed twice at being a keeper. Grover's last chance to win a searcher's license (so that he can go in search of Pan) is to safely bring Percy and Annabeth home from their quest. Which he does! Wahoo!
Grover's dream is to search for Pan, a privilege that only few satyrs are granted. You see, satyrs have a deep connection to nature and to everything in nature (all animals and creatures alike). They serve Pan, the god of wild places, but Pan has been missing for hundreds of years. Grover tells Percy the story:
When humans heard the news, they believed it. They've been pillaging Pan's kingdom ever since. But for the satyrs, Pan was our lord and master. He protected us and the wild places of the earth. We refuse to believe that he died. In every generation, the bravest satyrs pledge their lives to finding Pan. They search the earth, exploring all the wildest places, hoping to find where he is hidden, and wake him from his sleep. (12.17)
So, Grover's dream is to set out on a quest from which none of his satyr ancestors have ever returned alive. The G-man is one brave guy.
And he's incredibly passionate about nature. He's like the most loving environmentalist you've ever met. He is deeply saddened when he sees cans and garbage littering the New Jersey woods. And the sight of the neglected lion, zebra, and antelope with chewing gum in their hair, mismatched food in their pans, and a balloon tied to a horn truly breaks Grover's heart. He is able to place a "satyr's sanctuary" on these animals when he, Percy, and Annabeth free them into the streets of Las Vegas. A "satyr's sanctuary" is kind of like a protective charm that will ensure the animals make it into the wild safely. Grover's got a big huge heart.
For your information, Grover can die, but he'll be reincarnated. We learn this when Grover tries to convince Percy to leave him in the Underworld and to use a magic escape pearl on Sally Jackson instead of him:
"I'm a satyr […] We don't have souls like humans do. [Hades] can torture me until I die, but he won't get me forever. I'll just be reincarnated as a flower or something. It's the best way." (19.163)
This is interesting, because it totally seems like Grover has a soul to us. His capacity to love and to understand the world around him is pretty huge. The fact that he's even offering to stay in the Underworld in order to save Sally Jackson tells us that he is one generous, selfless dude.
As if Grover's tin can-eating, Pan-loving ways weren't enough to win you over, consider the fact that he is really good at reading emotions. Reading emotions is almost like his very own superpower. When Percy confesses to him that he only accepted the quest so that he might have a chance to bring his mother back from the Underworld, Grover sees right through Percy:
"Look, Percy, I'm not as smart as Annabeth. I'm not as brave as you. But I'm pretty good at reading emotions. You're glad your dad is alive. You feel good that he's claimed you, and part of you wants to make him proud. That's why you mailed Medusa's head to Olympus. You wanted him to notice what you'd done." (12.50)
Pretty wise words, if you ask us. Grover's got the 411 on everybody's feelings. In this way, he's almost as powerful as any god.