Surely, you don't think Geoff Johns (brilliant though he is) was the first to imagine Sinestro creating a corps of anti-Lanterns, do you?
John Broome did it in the 1967 cringe-worthy classic, "My Mastermind, The Car!", in which the spirit of Sinestro possesses "Goitrude", the former cab of the former Green Lantern's former sidekick, Doiby Dickles. Yes, really; could I make that up?
"In brightest day, in blackest night,
no justice shall escape my sight!
Let those who worship justice's might
beware my power,
Evil Green Lantern's light!"
Evil people have no regard for scansion and meter, folks (for example, have you ever read Maya Angelou?). Either that, or Sinestro hired William S. Gilbert to pen the oath.
Nah; that would have come out more like this:
"In brightest day, I dare surmise,
or blackest night, to all surprise,
all justice seen before my eyes
shall surely quake and quiver.
Then justice-lovers, softly simpering,
bow their heads in shameful whimpering.
Evil Green Lantern light come shimmer, bring
death, and doom deliver!"
Anyway, the reason you never heard of the Evil Green Lanter Corps (a.k.a. Sinestro Corps 1.0), is that it failed in the beta test... in one panel.
Yeah, back in the day, all it took was Alan Scott and Hal Jordan to defeat the entire Sinestro Corps, and they did it in one panel, rather than 12 issues plus special one-shots.