Venus

Venus was habitable, like Earth.
Astonishingly, the molten hell Venus as we know it, had liquid water flowing on its surface back then.

Venus had life before Earth and Mars, which makes it the first planet to have life in the Solar System. But the lifeforms of Venus weren't successful, as Venus's atmosphere thickened and trapped heat inside, dramatically making a greenhouse effect.

This caused a major mass extinction killed all the life forms on Venus, and is seemingly lost forever.