The greatest example of extra terristial life in the Marvel Universe comes to us courtesy of the rider of the spaceways - the Silver Surfer. Created by Jack "King" Kirby in 1961,  the Surfer has a tradgey that Oedipus himself would appreciate. 

Once upon a time,  the peaceful planet of Zenn-La was found by  the world devourer, Galactus, who sought to satisfy his awesome hunger. In a selfless act of courage, Norin Radd offers himself as a herald in order to save his world from destruction. Thus, the Silver Surfer roams the cosmos to find uninhabited worlds for his master to consume.   Sadly, Norin Radd has lost his beautiful Shala Bal, an is sentenced to roam the cosmos alone, never to return to the two loves of his life, his home and his soulmate. Only at the last minute I decided not to include animals from the Star Wars universe. The principles are the same when an artist must concieve of alien animals. Usually, they are a composite several  current  and/or extinct Earth creatures. In outer space, a great imagination is unlimited!