Before Crisis on Infinite Earths altered DC's continuity, Supergirl of Earth-One was a Kryptonian like her cousin Superman. While working on an antidote to Kryptonite, she accidentally created X-Kryptonite, a lost chunk of which gave her orange tomcat Streaky Kryptonian superpowers which had to be renewed periodically by re-exposure to X-Kryptonite, and neither he nor Supergirl knew where it was nor why he kept running into when a normal cat with only animal intelligence.