Venus, second planet outward from Sol in Sol System, and second to be colonized by Humanity, after Mars. When Earth's biosphere began failing, several companies, notably AphroCo (India), VeneraCorp (Indonesia), ExoLife, GeoBuild, and lastly RC3 (Космическая Колонизация России Корпорация).
Terraforming began at the time of colonization, in the 2080s, cloud cities orbiting, removing the sulphuric acid and extracting the carbon, a massive aluminum parasol shield Venus from the sun's heat, in an effort to cool the planet, and extract the carbon dioxide for use on Mars.
Oort Cloud bodies and asteroids are slung past Venus in tight orbit, causing the rotation rate to increase, and evaporating their mass into the atmosphere as a means to add water and to add reagents to further reduce the carbon dioxide load of the planet.
Many of these asteroids are further redirected to High Earth Orbit (HEO) for processing into ships for Earth's colonization efforts. When Warp Drive and Wormholes are discovered, interest in processing this sister planet to Terran norms wanes, but hardy colonists persist until The Fringe and The Core are well established.