Ash Ketchum is the main character in the show.  He is ten years old, and wants to become the greatest Pokemon Master in the world.  His first Pokemon was Pikachu, then he caught a Caterpie which evolved into Butterfree, Pidgeotto, Charmander which evolved into Charizard, Squirlt, and Bulbarsaur (who chose not to evolve).  His rival is Gary Oak, who always seems to be ahead of him.  In his journeys, Ash meets up with Misty and Brock, who join him.
 

Misty can act childish, stubborn, and immature, but out of the whole group, she knows the most about Pokemon.  She is a water Pokemon trainer, her Pokemon are  Goldeen, Staryu, Starmie,Horsea, Psyduck, and Togepy.  She follows Ash on his journey, always reminding him that he owes her a bike.  Misty and Ash are always fighting and never seem to get along, but deep down, they care about eachother.
 

Brock is the leader of Pewter Gym.  He joined Ash and Misty on their journey after his dad returned and offered to take care his brothers and sisters.  Brock is the oldest of the group, and, in almost every episode, he falls in love with another girl and tries to impress her.  But, he always fails.  Brock mostly raises rock Pokemon, he has an Geodude and an Onix.  Suzzy, a breeder, gave him a Vulpix and he takes extra good care of it.
 

Gary is Prof. Oak's grandson.  He is Ash's greatest rival. He is always bragging about his Pokemon, but we never see any of them.  I think his starting Pokemon was Eevee.  He is always ahead of Ash, and calls him a loser.

Team Rocket are the main villians in the show.  Jesse seems to be the leader of the three, with Meowth behind her, and James in the back.  Jesse thinks she's better than everyone else, and is rather bossy.  Jesse's Pokemon is Ekans, which evolved into Arbok when she showed that she cared about it.  James is the nicest of the three.  He is the son of a wealthy family that he ran away from because he didn't want to marry Jezebel (who looks exactly like Jesse).  James' Pokemon is Koffing, which evolved into a Weezing when James showed that he cared about it.  Meowth is the only Pokemon that can talk, and seems to boss Jesse and James around.