Pikachu is the Pokémon whose Pokédex number is as old as the Pokémon franchise

As part of its ongoing efforts to promote all things Pokémon, The Pokémon Company has shared a special post dedicated to Pikachu:

Did you know? Whenever Pikachu comes across something new, it blasts it with a jolt of electricity. If you come across a blackened berry, it’s evidence that this Pokémon mistook the intensity of its charge. This Pokémon has electricity-storing pouches on its cheeks. These appear to become electrically charged during the night while Pikachu sleeps. It occasionally discharges electricity when it is dozy after waking up.

Source: @Pokemon