He was making first contact with sentient aliens.

It takes place in the present day and describes the arrival on Earth of sentient aliens.

There is no sign of sentient aliens, but humans presume the invasion to be deliberate, either "seeded" from space or brought by undetected spacecraft.

How big a jump was it to then substitute a sentient human in place of a sentient alien?

He supposed that meant humans, as the likelihood of sentient nonhuman aliens was very slim.

A sentient alien, Riker thought, and unless there's some expedition I don't know about, the Federation's never even heard of this one.

"Do you know, I think I'm the first sentient alien they've ever encountered?"

The tavern was created after a race of sentient aliens called Chirpsithra landed on Earth.

The only contact humanity has had with sentient aliens?

The Outsider would be the first sentient alien ever to contact the human race.