Upon his 10th birthday, he broke his Voltorb-shaped alarm clock while dreaming about Bulbasaur, Squirtle and Charmander and slept late, causing him to lose all the Starter Pokémon to Gary and two other trainers. He was then forced to use the non-obedient Pikachu. They failed to capture Pokémon, and when he threw a rock at a Spearow, a flock of Spearow attacked them and Pikachu was injured. Ash then stole a bike from a girl called Misty and made his way to Viridian City's Pokémon Center, and Pikachu scared the Spearow away with a ThunderShock attack. He then saw a Ho-Oh flying over a rainbow.
He was then taken to the Pokémon Center by Officer Jenny where Nurse Joy took care of Pikachu. He called Delia and then Professor Oak and asked him about Ho-Oh, but mistook a picture of an Articuno for it. Team Rocket then attacked the Center with their Ekans and Koffing. Pikachu then combined it's energy with Nurse Joy's Pikachu to blast Team Rocket to the moon. He and Misty then made their way into the Viridian Forest, where Ash captured a Caterpie that evolved into a Metapod and then a Pidgeotto. After a battle with Samurai, Metapod was stolen by a Beedrill, but it evolved into a Butterfree.
In Pewter City, he encountered Flint and he decided to compete in the Pokémon League. He and Pikachu were then defeated by Pewter City's Gym Leader Brock and his Onix. Flint then helped Ash supercharge Pikachu and he eventually got a Boulder Badge(but not for winning). Flint then revealed he was Brock's father and he allowed Brock to travel with Ash. After saving some Clefairy at Mt. Moon, they went to Cerulean City despite Misty's protests to go to Vermilion City and he found out that the three Gym Leaders were Misty's sisters and they had turned it into a water Pokémon circus. He then battled Misty, but got the Cascade Badge for saving the Gym from Team Rocket.
Ash then captures a Bulbasaur, Charmander, Squirtle, Krabby, Primeape Muk, and 30 Tauros. He also uses a Haunter to battle Sabrina, but later gives it to her. Charmander also evolves into a Charmeleon, and later a Charizard. However, it refused to obey him. He eventually releases Butterfree to date a Pink Butterfree. He wins a Thunder Badge, Marsh Badge, Rainbow Badge, Soul Badge and Volcano Badge. He then returns to Viridian City and finds Gary already has 10 badges. Gary challenges the Viridian Gym Leader first, but Ash and the others sre distraced by trying to find Misty's Togepi. When they got in, Gary had been beat by Giovanni and Team Rocket was in control of the Gym. Ash battled Jessie with Giovanni's Machamp, Kingler and Rhydon. Jessie refused to give Ash the Earth Badge, but Ash got it when they "blasted off".
They then returned to Pallet Town and asked Oak where the Indigo League was taking place. He revealed it was taking place at the Indigo Pleateau, and Ash competed two months later. Krabby and Ash battled together for the first time and Krabby evolved into Kingler, getting Ash to the Top 16, one further than Gary, in the Indigo Conference. He even made a new rival, Ritchie and Ritchie beat Ash when Charizard refused to battle Ritchie's Pikachu, Sparky. Ash then returned to Pallet Town after Ritchie loses the Top 8.
During a party, Team Rocket attacks and Pidgeotto is poisoned. They are soon attacked by the flock again, with the leader having evolved into Fearow. To protect some Pidgey and Pidgeotto, Pidgeotto evolves into Pidgeot and defeats Fearow, but Ash fails to capture Fearow and leaves Pidgeot in charge of the Pidgey and Pidgeotto. Oak then sends Ash to the Orange Archipelago to pick up a Poké Ball called the GS Ball from Professor Ivy, but they crash the blimp they're travelling on on Valencia Island. Brock then stays behind to help Ivy, and Ash and Misty are forced to travel alone. They they find a boy named Tracey taking care of a baby Lapras on Tangelo Island and Tracey comes with Ash when Ash decides to compete in the Orange League. He then catches the Lapras.
He defeats Cissy on Mikan Island and earns a Coral-Eye Badge and then Danny on Navel Island and earns a Sea Ruby Badge. He also catches a Snorlax and Charizard finally obeys Ash after being frozen by Tad's Poliwrath. He then beats Rudy on Trovita Island and earns a Spike Shell Badge and then Luana (who thought Ash is her son Travis) on Kumquat Island, earning a Jade Star Badge. He then beats the Orange League Champion Drake and becomes Orange League Champion. On his way home, he finds Lapras' herd and returns Lapras to it.
He then returns to Pallet Town again and finds Brock working for Delia and delivers the GS Ball to Professor Oak. Team Rocket trires to steal the Poké Balls from Professor Oak, but they are defeated by Gary's Nidoqueen and Ash has his first battle with Gary: Pikachu against Gary's Eevee and lost. Ash then learned Gary was heading for Johto and followed him, with Brock rejoining him and Misty and Tracey stayed behind to become Professor Oak's assistant.
He saves a Totodile from Team Rocket and enters for the Johto League, capturing a Heracross, Chikorita, Cyndaquil, Totodile and a rare shiny Noctowl. He earns a Zephyra Badge, Hive Badge, Plain Badge, Fog Badge, Storm Badge, Mineral Badge, Glacier Badge and a Rising Badge. Chikorita evolves into a Bayleef and shortly before his eighth badge win, he wins a Pokémon Egg after beating Gary's Arcanine in a contest that later hatches into a Phanpy. However, Charizard stays at Charicific Valley, Squirtle returns to the Squirtle Squad and Bulbasaur becomes an ambassador to Professor Oak's Laboratory.
Shortly before arriving at the Silver Conference, Professor Elm asks Ash to pick up another Pokémon Egg from the Naomi and he bumps into his Lapras, now a fully-grown Lapras. The egg hatches into a Larvitar and he eventually is scked into Larvitar's mind by an Unown and finds out the Pokémon Poacher Brothers stole Larvitar's egg from it's mother Tyranitar and which is why it is afraid of humans. They break the branches and then reunite Larvitar and Tyranitar on Mt. Silver. They defeat the Poacher Brothers and Larvitar is then left with Ranger Mason on Mt. Silver.
He then meets a trainer from Hoenn called Harrison who has also decided to enter the Silver Conference. He then does a round-robin match against a Fire-type trainer called Macy and beat her with aid from Squirtle before facing Jackson with aid from Bulbasaur and making his way to the Victory Tournament. He defeated Gary with aid from Charizard, but then lost to Harrison. He watched Harrison lose to Jon Dickson and then talked to him before Gary told him he wanted to become a Pokémon researcher.
He then got left by Misty and Brock before seeing Ho-Oh again. He then decided to leave for Hoenn and left every Pokémon but Pikachu at Professor Oak's Laborotory. However, during the travel, Team Rocket attempted to steal Pikachu and Pikachu got a Pokémon illness when tossed into their Electromagnet.
After learning that there is no Pokémon Center in Littleroot Town, Ash goes to Professor Birch and Pikachu runs off, so they go after it. Eventually, Pikachu gets caught in Team Rocket's new robot and drained of the excess electricity and restored to normal. They then go with their new friend May to challenge the Hoenn gyms.