Since exoplanets are all the rage these days (more to come), then let's follow what I consider a logical conclusion: That life is fairly common out there, and some small percentage of it is smart. Smart enough for clothes, for art. And given that the same physical laws apply everywhere, then planets of similar size and distance from their star, with similar chemical composition, with water, etc, will likely evolve fairly common lifeforms as here on Earth - they'll eat, reproduce, try and maximize resources, and die. Certain mechanical designs will play out in completely independent environments - how alien would alien ocean life forms look, for example? There's only so many ways to swim, or navigate on land. Maybe they have 4 arms instead of two, or tentacles instead of hands, but I don't think the differences will be that extreme - like, for counter example, a life form made of energy, or gas, or some kind of ooze, etc.
And thus, to conclude: The Gorn. Reptile-like alien lifeforms. And why not? Way back when, a smart alien lizard learns to really exploit a niche, swells in numbers, evolutionary pressures produce ever refined hunting techniques leading to tools, to fire, to technology in all its forms. There's nothing at all which says one life form or another could not become dominant in a given environment. For example, perhaps ocean worlds have super intelligent dolphin like aliens. Who knows!
The sky is literally the limit - and by sky, I mean everything.
