Ash- Ash is a boy from pallet town who wants to become a Pokemon Master. He is the main protagonest of the story unless you want to count Pikachu, Ash's first Pokemon. Ash matures as the story goes along, and he starts becoming a better person and trainer. He likes his Pokemon to always be his friends and sometimes gets into trouble with his lack of Pokemon knowledge, but he develops very good strategy to make up for it.
Brock- Brock is a girl crazy guy from Pewter City. Once the Pewter City Gymleader, Brock left his home of many little brothers and sisters to become the Best Pokemon Breeder. Brock is the oldest of his brothers and sisters and took care of all of them until his dad showed up and told him to follow his dreams. Brock likes to cook, clean, and breed Pokemon. He specializes in Rock Pokemon, but he likes to breed all kinds. Did I mention he likes girls?
Professor Samuel Oak- A famous Pokemon reaseacher, who gives both Ash and Gary thier first Pokemon. A friend to Ash, and grandfather to Gary.
Gary- Ash's Rival and Professor Oak's grandson. Gary is a smart Pokemon trainer in that he knows lots about Pokemon before he ever starts on his Pokemon Journey. Gary always thinks ahead and trains his Pokemon well. He's changed his attitude a bit, and now is a very respectable, good trainer.
Tracy- a Pokemon watcher- one who watches observes and sketches or draws Pokemon. He's a fan of Professor Oak and joins Ash and Misty on their journey so he can meet Prof. Oak in person.
May- the daughter of Gymleader Norman who starts her Pokemon journey in the Hoenn region loving traveling more than Pokemon. She begins her journey not knowing a whole lot about Pokemon. Eventually, she decides that she wants to be a Pokemon Coordinator instead of a Pokemon trainer. A Pokemon Coordinator specializes in trying to win Pokemon Contests. Contests test Pokemon in the categories: Cool, Cute, Beauty, Tough, and Smart.
Max- May's younger brother who is not old enough to be a Pokemon trainer. He's has lots of Pokemon knowledge, and wants to be a gymleader when he grows up, like his dad.
Drew- May's rival, a Pokemon coordinator, who even beat Ash in battle. Round 1 in a Pokemon contest may be a solo preformance, but round 2 is a 5 minute pokemon battle. Thus Drew, like any great coordinator, is a skilled Pokemon trainer who can battle with style.
Officer Jenny- There are many Officer Jennys in the tv show Pokemon. All seem to be related to each other somehow. Normally the only Police officers around are Officer Jennys.
Nurse Joy- Every Pokemon Center (a medical center or hospital for Pokemon) has their own nurse Joy. Like Officier Jenny all the Nurse Joys seem to be related somehow. Some Nurse Joys don't work at Pokemon Centers.
Mrs. Ketchum- Ash's mom. She cares for Ash.
Giovanni (the boss)- the Veridian City Gymleader who gives out the earth badge, and the boss of Team Rocket whom Jessie, James, and Meowth work for, trying to catch rare and unusual Pokemon. How he created/started Team Rocket is a question that puzzles me. Team Rocket refers to him a lot, but he doesn't appear much.
There are many other characters that appear for multiple episodes, but the characters above, Jessie, James, Meowth, and Misty are the main characters of Pokemon. (Atleast I think so)
Here are a few other characters that appear more than once:
Butch- a member of Team Rocket that has green hair.
Cassidy-Butch's Team Rocket partner, met Jessie a long time ago. Together Butch and Cassidy are rivals of Jessie James and Meowth.
Cassy- Heroine of the Crystal version of Pokemon. Starts her Journey as a Pokemon trainer in Johto. Cassy is a major fan of the Electabuzz baseball team, and loves yellow Pokemon with stripes.
Dulplica- wants to be the greatest Ditto master. (Ditto is a pokemon that can 'transform' into anything including other Pokemon)
Richie- a Pokemon trainer whom Ash first meets at the Indigo Plateu.
Todd- a famous young Pokemon Photographer.
Misty Back to Pokemon Main Jessie and James