P.imperator hails from west Africa and is one of the largest scorpions, reaching a length of around six or seven inches. It has a glossy black back and claws, with lighter purplish areas on the sides and on the joints. It has sparse, short hairs on the claws, I do not know what these are for.
P.imperator is the most common species of scorpion in the trade, due to its large size, interesting appearance, ease of care, relative docility, and mild venom. The fact that it can be easily captured in quantity in its native habitat and is fairly easy to breed in captivity probably has something to do with this as well.
P.imperator has a comparatively mild sting, supposedly it is quite similar to a bee sting, both in terms of pain and lasting damage (none, unless you're allergic, in which case you're screwed). You hand (or whatever) will swell up as well. All of this is second hand, I have never been stung. Even so, don't handle them unless absolutely necessary, such as cage cleaning or removing a pregnant female if you are housing them communally. As strange as it sounds, the best way to pick them up is to grab them by the stinger with two fingers, they can't sting you and they can't whip up and get you with the claws.
Never pick up a wild scorpion unless you're willing to bet your life that it's harmless.
A 5 or 10 gallon aquarium with a screen lid will suffice for one to three emperors. These are not particularly active animals, they do not need a large cage.
Temperature should be kept at around 75-85°F during the day, and can be safely dropped to 70°F at night. Do not let it get cooler than that, they are tropical animals and do not tolerate cold.
Humidity should be kept around 75%, mist twice daily to keep it at that level.
Bark, peat, sphagnum, and various mixes of the above will all work as substrate. They like to dig, the substrate should be at least 3" deep to allow for this.
Cork bark and plants (real or artificial) should be used as hidespots. Dry leaves will work as well.
A small, shallow water dish should be provided.
They can be kept communally if there is enough space and food. If you wish to breed them, pregnant females should be removed and kept seperately.
A carnivore, P.imperator should be fed mainly crickets and mealworms. Around three or four per animal per week will suffice. Larger specimens may take pinkie mice, but this is unnecessary (not to mention really, really cool to watch).
I do not know how to induce them to breed in captivity, however if you look around you won't have to. Pregnant females are frequently imported, look for one that looks fat. Eventually you'll have a female scorpion that is carrying around a couple dozen tiny white babies or her back. They remain there for a couple months until they assume the glossy black color of the adults and go out on their own. I do not know how long it takes for them to reach full size.
Let my know if you see any inaccuracies or feel anything was left out. Feel free to post you own experiences and pictures and what-not.