Our descendents will do this, unless we discover Earth-like worlds around other stars, and a technology to travel there.
I like Carl Sagan's concept (the subject of his doctoral thesis) of terraforming Venus. This would take centuries, far longer than Mars.
Venus would be much more difficult. There's no water on Venus (Mars has some in the icecaps and probably underground) and has 1000 times the atmosphere we'd need, not to mention it's all CO2. Plus, since it is closer to the Sun, it would be difficult to cool it off enough to be habitable.
Venus would require a lot more-solar shades and removing 98% of the atmosphere and taking the Oxygen out of the CO2...but in a few centuries, maybe. Even if we could accept a hotter planet to live on, we'd need shading on Venus otherwise we'd all sunburn like crazy since sunlight is double the intensity on Venus as here on Earth. On Mars it's half (44% actually) so that's another challenge.