Bulbasaur was raised in the Hidden Village by Melanie, who cared for sick, injured, and abandoned Pokémon. Bulbasaur acted as the village's bodyguard, but after Ash helped defend the Hidden Village from an attack by Team Rocket, Melanie encouraged it to join Ash, explaining that its growth was being stunted by staying too long in the village. Although Bulbasaur initially appeared to distrust Ash, it agreed to join him. In Island of Giant Pokémon, it alone assumed that Ash had abandoned it and the others. Its views on Trainers were presumably colored by all the abandoned Pokémon in the Hidden Village. Over time Bulbasaur grew to trust its new Trainer.
Bulbasaur is extremely stubborn, surly, and eager to battle. Although his surliness has lessened. He battled against Erika's Tanglea and lost, but redeemed himself when battling against Aya's Venonat, where he sent Stun Spore back at it with Whirlwind and beat it with Leech seed. He had the opportunity to evolve after battling a powerful Rhyhorn with a very strong Take Down attack in Bulbasaur's Mysterious Garden, but refused at a mass of Ivysaur as well as a Venusaur because he doesn't want to evolve at the Bulbasaur evolutionary festival. This allowed him to learn the powerful Solar Beam technique. Venusaur finally understand, but he say Bulbasaur will be evolved if he wants to.
He has the heart of a fighter and he never gives up in a battle. He has the determination to keep fighting even if the odds are against him, defeating such varied opponents such as a herd of Exeggutor, despite the disadvantage. He also beat Jeanette Fisher's Beedrill with Tackle, and went on to battle Scyther despite the type disadvantages. After some trouble, he used Vine Whip to hit every Double Team clone and then hit the real Scyther with both vines knocking it out. Ash tried for the sweep with Bulbasaur, but he fell to her surprisingly strong Bellsprout. On one occasion Bulbasaur, along with Pikachu, was briefly lent to Misty to allow her to compete in the Princess Day Festival with a more balanced team, Bulbasaur single-handedly winning her first match by defeating a Kingler, Pinsir, Cubone and Raticate on its own.
Bulbasaur was also used to battle against Drake, the Orange League Champion, and his Electribuzz. Bulbasaur is undamaged by Thunder Shock and hits it with Razor Leaf. Bulbasaur then lands a Tackle, but is knocked out by ThunderPunch.
Bulbasaur was used to capture Heracross, who started sucking sab from his bulb, much to his annoyance. Bulbasaur became the only member of Ash's original team, save for Pikachu, to remain in his care, while he watched his best friend Squirtle and companion Charizard leave.
It battled against a wild Chikorita that Ash wished to capture. He was also used to fight Team Rocket, but was annoyed by Heracross, who was sucking the sap from his bulb. It was also used to battle Misty to decide who gets to keep Totodile. Bulbasaur looked set to beat her Poliwag with Razor Leaf, but it evolved into Poliwhirl and hit him with Bubble. Bulbasaur then flattened Poliwhirl with SolarBeam, winning the match for Ash. He also had a rematch with Aya and crippled it with Leech Seed once more, but this time, Venonat came back and almost won with Supersonic and Tackle, but Bulbasaur knocks it out with Body Slam.
Bulbasaur had stayed with him until midway in the Johto adventures, when he was sent back to Professor Oak's to keep the Pokémon there from quarreling with each other. He saved an Oddish from a falling boulder, and stopped the grass and water type Pokémon from quarreling by ordering the construction of a new lake.
Bulbasaur came back alongside his friend Squirtle in the Johto League, where Squirtle was mocked by Jackson's Azumarill, as well as being slapped in the face. Bulbasaur calmly restrains them, but the better half of the duo joins the fray when Jackson's Meganium mocks him. He battles against Jackson's Magneton, who had defeated two of Ash's Pokémon in the 3-on-3 match. Bulbasaur learned from Pikachu and Cydaquil's mistakes, and despite being the most disadvantaged one out of the three, he takes the win with Leech Seed and Vine Whip. He then battled against Meganium, who he still had a bitter rivalry. Despite Bulbasaur being tired from the previous battle while Meganium is healthy, Bulbasaur dodges Body Slam an lands a Razor Leaf, while being hit by Meganium's Razor Leaf. He reverses it's Body Slam by usiong Vine Whip around its neck and pelts it with Razor Leaves and Vine Whips, before a double SolarBeam takes them both out, resulting in a tie for the two trainers, and Ash advancing to the next round.
Bulbasaur later returned in Hokey Poké Balls to meet May's Bulbasaur, and the two hit it off. When Jame's Cacnea proves too strong for May's Bulbasaur, Bulbasaur defeats both Cacnea and Jessie's Serviper with Vine Whip. In The Right Place and the Right Mime, May decides to leave her Bulbasaur with Oak so she can learn from Ash's.
He returns again alongside Charizard and Squirtle to battle Brandon at the Battle Pyramid, and battled against Brandon's Dusclops. Although Dusclops managed to bring down Charizard, Bulbasaur was able to endure the unavoidable Shadow Punch and land a hit with Leech Seed, but struggled to overcome the Confuse Ray/Mean Look combo. Ash snapped him out of the confusion and defeated it with Solar Beam. Solrok's Psychic attacks were tougher to overcome, but in the end, both Pokémon were knocked out with a double Solar Beam.
Bulbasaur reappears in An Old Family Blend! in Professor Oak's Laboratory, where Heracross is sucking sap from his bulb, much to Bulbasaur's annoyance. He used Vine Whip to shove Heracross away.
Bulbasaur reappeared in a flashback in The Fires of a Red-Hot Reunion!
Bulbasaur is frequently viewed as the responsible leader of Ash's Pokémon, especially due to his actions at Professor Oak's lab. He is also a Pokémon Ash values more than most of his other Pokémon, possibly because he always wanted to catch one, as explained in Bulbasaur and the Hidden Village, although he was his second choice as a starter, after Squirtle. He also formed a bond with Pikachu and Squirtle while they fought together while part of Ash's team. But, at the start he disliked trainers as shown in island of the Giant Pokémon where he said, "Maybe Ash has forgotten about us."
Bulbasaur's best friend in the group is Squirtle, who's immature, fun loving personality contrasts with Bulbasaur's serious, mature one. Nonetheless, all of Bulbasaur's immature acts have something to do with Squirtle, such as Bulbasaur beating up Squirtle after he ate his cookie, or using Squirtle as a sled after witnessing other Pokémon enjoying themselves on actual sleds. When Squirtle was leaving Bulbasaur looked away while shaking hands/vines, sad to see his friend go.
|Tackle||Bulbasaur and the Hidden Village|
|Vine Whip +||Bulbasaur and the Hidden Village|
|Razor Leaf +||Primeape Goes Bananas|
|Leech Seed +||The Ninja Poké-Showdown|
|Solar Beam +||Bulbasaur's Mysterious Garden|
|Sleep Powder||Misty Meets Her Match|
|Take Down||The Grass Route|
|Dig -||Bulbasaur...the Ambassador!|
|+ indicates this Pokémon used this move recently.*|
- indicates this Pokémon normally can't use this move.
- Bulbasaur is the first starter Pokémon Ash ever captured.
- Bulbasaur was the first -Type Pokémon that Ash has owned.
- Bulbasaur is the second Pokémon Ash owns that chose not to evolve, the first being Pikachu, but he is the first Pokémon that Ash caught that chose not to evolve because Bulbasaur was not ready to evolve yet. Pikachu wants to prove that he can defeat stronger Pokémon without evolving.
- Bulbasaur is possibly the de-facto leader of Ash's Pokémon that are at Prof. Oak's lab.
- Bulbasaur is the only one of Ash's original six Pokémon, (other than Pikachu since Pikachu is always with Ash,) that he still has.
- Despite being part Poison-type, Bulbasaur does not know any Poison-type moves.
- Bulbasaur, after Pikachu, is the Pokémon Ash has owned for the longest time period. It is the only member of Ash's original team, besides Pikachu, to remain in his care, and the only one to reside at Oak's lab.