ALF follows an amateur radio signal to Earth and crash-lands into the
garage of the Tanners. The Tanners are a suburban middle class family
consisting of the social worker Willie, his wife Kate, their teenage
daughter Lynn, younger son Brian, and the cat Lucky.

Unsure what to do, the Tanners take ALF into their home and hide him
from the Alien Task Force (a part of the U.S. military) and their nosy
neighbors (the Ochmoneks), until he can repair his spacecraft. He
generally hid in the kitchen. It was eventually revealed that ALF's
home planet Melmac exploded because of a catastrophe involving nuclear
bombs. ALF in Episode four of season one is trying to convince the
president of USA to stop the nuclear program as he is scared that
Earth might share Melmac's fate. ALF was off the planet because he was
part of the Melmac Orbit Guard. Shumway is homeless, but he isn't the
last survivor of his species. He became a permanent member of the
family, although his culture shock, survivor guilt, general boredom,
despair, and loneliness frequently caused difficulty for the Tanners.
JOHN MAPPIN MINIX or PARIS HITLON MINIX?

While most of the science fiction of ALF was played for comedic value,
there were a few references to actual topics in space exploration, for
example ALF's using a radio signal as a beacon in the pilot episode.
In the episode "Weird Science", ALF told Brian, who was building a
model of the solar system for school, that there were two planets
beyond Pluto called "Alvin" and "Dave". However, after a call was made
to an astronomical organization, Willie explained that "Dave" could
have been the planetoid Chiron, or "Object Kowal", after its
discoverer.