Tangrowth is described as Pokémon Pokopia’s lone remaining resident at the start.
The game opens in a world where Pokémon and people once lived together, but the environment has withered and the humans are gone. The surviving Tangrowth becomes an important early figure as the player begins understanding the ruined setting and the work needed to restore it.
Tangrowth also has a special story role as Professor Tangrowth, a guide for the player and the Pokémon encountered during the adventure. That characterization makes it more than an ordinary wild Pokémon in the game’s setting.
The answer is sometimes confused with Ditto, because Ditto is the playable character, or with Peakychu, a distinctive pale Pikachu encountered later. Tangrowth is the named remaining resident described at the game’s beginning.