Deoxys, also known as Entity 1, is a legendary Pokémon. Its name derives from the word Deoxyribonucleic Acid (DNA). Since it is the DNA Pokémon, the name fits it perfectly. There are two entities with the name Deoxys. Entity 1 is weaker than Entity 2.
An alien virus exposed to laser beams mutated into two lifeforms: Deoxys (Entity 1) and Deoxys (Entity 2). Entity 1 was used by Team Rocket to fight Red in order to lure the other Deoxys out of its hideout. After Deoxys 2 was captured, Team Rocket didn't need Deoxys 1 anymore, so they trashed it.
Deoxys has the ability to transform into 4 different forms: Normal Form, Attack Form, Defense Form and Speed Form.