Let’s suppose one day you’re home by yourself and you hear a strange noise outside. You take a look and see a UFO landing. One of those creepy looking grey aliens (with the giant black eyes) gets out and gives you a friendly wave.
Some ground rules:
The alien can understand you and carry on a meaningful and sophisticated conversation however he (she/it) does not necessarily know or understand everything about how you and your world work.
The alien may be willing to share his technology with you but how you ask will inform his opinion on humanity. So if you decide to ask him to help you take over the world, he reserves the right to flip you his equivalent of the bird and take off.
Although you are the alien’s tour guide, he has every right to abandon you if he no longer finds you useful. Therefore, if you take him to Lawrence Livermore and you can’t even get past the gate (while he is ushered away by astounded scientists) you can assume your usefulness to him is at an end.
Aside from his UFO (which can cloak) and immunity from death, the alien doesn’t have any special powers like mind control or whatnot. The UFO only has room for him so unless you agree to meet him somewhere, he gets around your way, not vice versa.
The alien is your guest for as long as you wish. What do you do with him?