's pet cat.
Streaky is a normal earth cat. His powers are gained from exposure to
Kryptonite-X, a version of Kryptonite that was created in a
lab. Kryptonite-X was an attempt to create a cure for Kryptonite
poisoning. However, when Supergirl was exposed to Kryptonite-X, she
became sick in the same way as if she had been exposed to green Kryptonite.
The sample of Kryptonite-X was then disposed of. Streaky came into
contact with the Kryptonite-X and gained all of the powers of a
Kryptonian under a yellow sun (flight, super-strength,
super-speed, invulnerability, enhanced vision, etc.). The effects
of Kryptonite-X are temporary, but the sample ended up in Streaky's
yarn ball, and therefore, his powers were constantly recharged.
Supergirl never discovered where Streaky's powers came from.
Streaky was a member of the Legion of Super Pets.