Q

Q poses as a god from a race known as Q in the Q Continuum. He appeared to Starfleet vessels in the years 2360-2370. All StarFleet personnel are briefed on his existence.  He placed humanity on trail in 2364. Jean-Luc Picard and his command crew represented humanity, to the best of their abilities.

He accused humanity to be a savage race; Jean Luc managed to strike a deal and submitted to a test of conduct. The test was Farpoint Station, where the Enterprise manages to free a space bourne alien, whose mate was causing havoc on the citizens of the planet.

Q and his specie create games, or test as they may be seen as, to understand and study the human race more efficiently.

In his third appearance, he expressed interest in joining Picard crew. His reason is that humanity would go into uncharted levels of space and they would need help traversing the terrain. He even offered to renounce his powers to prove this was of genuine concern. However when Picard declined, Q put the Enterprise in the path of a Borg cube.

In 2366, he was stripped of his powers and made human by the Continuum. Q chose to be on the Enterprise. He requested asylum as well as protection from the beings he tormented.