Defender is an arcade video game developed and released by Williams Electronics in February 1981, and Revenge of Defender is an Amiga game based on original Defender by Epyx at 1989.
>In this sidescrolling Defender-like game you fly your starbike around the lunar landscape and collect Orolas. That’s small green aliens to you and me, and they’re really good for making perfume and catfood. You have to collect them from each level and dump them into a teleporter to send them back to your ship. When all aliens are collected you carry the last one to your lunar module and take off for another level. The number of aliens you have to collect on every level varies and you can leave the planet without collecting all the aliens but you will not get a bonus if you do so, and your task will only be more difficult as you get more enemies on the next level.