Ash's Venusaur (Aura)

Ash's Ivysaur was the fourth Pokémon caught by Ash Calem Ketchum during his travels through Kanto, and the first of the original starter Pokémon that Ash acquired.

Kanto
Bulbasaur lived in the Hidden Village with Melanie, where he helped her care for sick and injured Pokémon. Though distrusting of humans, Bulbasaur soon came to trust Ash enough so as to want to travel with Ash so he could grow.

Bulbasaur was instrumental in the battle to free the people aboard the S.S. Anne against Team Rocket. When Ash battled against the Vermilion City Gym Leader Lt. Surge, Bulbasaur was used against Lt. Surge's Voltorb. Though both Bulbasaur and Voltorb put up a good fight, they both managed to knock each other out.

Bulbasaur was later used to help capture a Krabby, later used against Cassidy and Butch's Raticate and Primeape at the Celadon Power Plant. Bulbasaur was then knocked out by the Drowzee Team Rocket used to control the Magnemite and Magneton.

Bulbasaur was used in Ash's Gym Battle with the Celadon City Gym Leader Erika, where he squared off against her Victreebel. Though Bulbasaur managed to learn Solar Beam, he only managed to tie against Victreebel, knocking both Pokémon out. Bulbasaur felt bad after that, and vowed not to evolve until he could prove to be as strong as any Bulbasaur could be. He was later present when Ash and his friends went to liberate the Silph Company of Team Rocket. Though he helped put up a good fight, he was no match for Giovanni's Rhydon.

During Ash's 11th birthday, Bulbasaur ate cake with Oddish and Squirtle. Bulbasaur would later be among the many Pokémon to keep Ash and Serena warm in a cave during a snowstorm. Some days later, Ash sent Bulbasaur to Professor Oak's lab to settle a feud between Pokémon on the ranch.

Bulbasaur would later be used in Ash's gym battle against the Viridian City Gym Leader and Team Rocket Boss Giovanni. The villain's Dugtrio managed to knock out Wartortle, but Bulbasaur managed to tie against Dugtrio. Bulbasaur would later be among the Pokémon on New Island that Mewtwo made a clone of, and made to fight against his own clone. Bulbasaur's tears upon seeing Ash dead was enough to revive his trainer.

During Round Two of the Indigo Plateau Conference, after Dratini beat Jeanette Fisher's Beedrill, Ash would use Bulbasaur against Jeanette's Scyther but lost.

Orange Islands
Bulbasaur was among the Pokémon who attended the party for Ash in Pallet Town. He would later be among the Pokémon who try to protect Ash and friends from the flock of Spearow that they ran into before that were being led by Fearow.

Later on Tangelo Island, Bulbasaur joined Ash's other Pokémon on the beach. On Mandarin Island, Bulbasaur would be among the Pokémon who participated in Ash's Pokévision video. On Trovita Island, Bulbasaur took part in a target game. Bulbasaur would later be used in Ash's gym battle with the Kumquat Island Gym Leader Luana, along with Wartortle and Dratini. Following Ash's 12th birthday, Bulbasaur would later try to help Ash and his friends free Moltres and Zapdos from Lawrence III.

Weeks later, Bulbasaur was used in Ash's battle with the Pummelo Island Stadium Supreme Gym Leader Drake. After Primeape was defeated, Bulbasaur was used against Onix. During this battle, Bulbasaur finally evolved into Ivysaur and defeated Onix, and tied with Drake's Electabuzz.

Personality and characteristics
Even as a Bulbasaur, Ivysaur is one of Ash's most mature Pokémon, and is frequently viewed as the responsible leader of Ash's Pokémon, especially due to his actions at both Melanie's Hidden Village and Professor Oak's lab.

Unlike his closest friend, the boisterous and immature Wartortle, Ivysaur was cautious bordering on cynical of all Trainers when he joined Ash's team, going so far as to physically attack Serena when he thought she was trying to take Oddish away. Over time, Bulbasaur grew to trust his new Trainer, but he retained a stubborn, surly, and eager-to-battle demeanor.

At first Bulbasaur didn't want to evolve until he was ready. Upon evolving into Ivysaur, he chose to remain as he is until he feels he is ready to become Venusaur.

Although Ivysaur is one of Ash's most mature Pokémon, he has succumb to fits of immaturity when Squirtle/Wartortle is involved. This is shown multiple times in disagreements or quarrels between the two.