Peter Lance is an alien from the planet Tharb. He is a member of the crew of a spaceship that is circling above the Earth to study our customs and learn more about us before announcing their presence. Exactly what their long term goals are is not really revealed and certainly not that important to the actual stories.
To get a closer look, and to get a better feel for the activity called sex, the leader, Dr. Kraag, sends crewman Pritan Lansol to the surface. With a few minor adjustments, Lansol becomes the human Peter Lance.
Lance's main purpose is to study sex but in doing so, he encounters beautiful women who keep getting into trouble, forcing Lance to step in and use his amazing physical prowess, telepathic abilities, and alien technology to defeat the bad guys and save the damsel. All so his research can continue, of course.
In addition to being a spy for his planet, Lance's adventures also put him into contact with and partially working with agents from the CIA. They may not know they are employing an illegal alien but they know that he gets the job done and that is all that matters.
And Peter Lance is given a lot, truly a lot, of chances to carry out Dr. Kraag's instructions to learn all he can about sex. Of course for him, a lot of activity is never a problem. Since the planet Tharb is a Jupiter-size planet with similar immense gravity, the muscles and endurance of its citizens are tremendous compared to Earthlings. This make him able to perform many activities for hours and hours.