Some of the coolest space/sci-fi toys came out during the 1960s, and these little guys are a perfect example. They are tiny (under one inch tall) space aliens made by an old company called Giant, which produced different varieties of toy soliders, vehicles and other small plastic toys.
According to this very informative article on the Plastic Solider Review website, the Giant company started out as the Rosenberg Toy Company in the 1940s, and then changed to Giant in 1960. By the end of the 1970s, it became known as Arco. I'm not sure the exact year Giant produced these aliens, but I'd guess sometime in the mid-'60s.
The aliens came in six different sculpts and three different colors -- green, brown and pink/purple. They are made of hard plastic. I love their simple yet very fun designs; they have a lot of detail and personality for being so tiny. They came with little circular UFOs they could be placed inside.
Giant also produced a line of micro astronauts and spacecrafts called Space Knights, so kids could set up space landings for discovery of these little weirdos on different planets. You can see all of these different pieces on Plastic Soldier Review linked above.