In a forest outside of New Bark Town, Ash solved a territory dispute between the local Heracross and Pinsir. Afterwards one of the Heracross who grew fond of Ash and his Bulbasaur decided to accompany him on his Johto journey.
Ash's Heracross is a strong, loyal and docile Pokémon whose feats of strength include lifting a big mechanical Pinsir and defeating Gary Oak's Magmar at the Silver Conference despite a type disadvantage. It loves to eat sap and nectar, which is often the main motivation for its actions: it may appear to be acting brave or heroic, only to later reveal that it was trying to get some food. Heracross often tries to suck the nectar out of Ash's Bulbasaur's bulb, much to Bulbasaur's annoyance.
Heracross was sent to Professor Oak in exchange for one of his Tauros, however, when Ash wanted to trade back Professor asked for more time to study Heracross to which Ash agreed. Heracross was eventually recalled and it competed with Ash as his trainer in the Silver Conference but remained at Oak's Laboratory when Ash departed for the Hoenn region.