Tomohiro Nishikado, the creator of Space Invaders, was working for Taito in the late '70s. When trying to come up with a new game idea, he looked to the popular brick-breaking games of the day for inspiration. He told the BBC he wanted to create a shooting game along that vein.
“Initially I started with tanks, then tried warships and warplanes — but the movement and animation didn't match the game,” Nishikado said in The Guardian. “After much trial and error, by far the best match were soldiers, but shooting people was frowned upon. It was at this time, while I was stuck for an alternative, I chanced upon Star Wars and realized I could use aliens because no one would complain about shooting them.”
For the actual design of the aliens, he chose to emulate the octopus-like Martians in The War of the Worlds. The result was the first fixed shoot 'em up (or schmup), providing a template for many titles to come.
Without Taito's restriction on human targets, Space Invaders might not have happened — or at least, not in the form that fans recognize. Space Invaders went on to revitalize a sagging home console market in 1980 and kickstart the industry as (arguably) its first true phenomenon.