20 Essential Comic Issues You Must Read Before You Die
15. Green Lantern #188
Another issue where the focus is more on the backup story (although the main story of John Stewart revealing his identity to the world is still pretty good), #188 introduced one of the most iconic Green Lanterns of all time.
The classic story Mogo Doesn't Socialize details the attempts of the evil alien Bolphunga to track down and kill the green lantern Mogo. After spending weeks looking for him on a harsh alien world, he eventually discovers the truth and flees in terror. The planet itself is Mogo.
It's a fun story that also runs with the idea that any sentient life form can be a green lantern.