I'm sure you guys know this story. King Kong's co-creator Willis O'Brien came up with this idea in the late 50's and penned a detailed plot outline where King Kong would battle a huge monster created by Dr.Frankenstein's grandson. Producer John Beck ended up stealing this from O'Bie, got George Yates to pen it into a screenplay and renamed it
King Kong Vs Prometheus (because it was believed Universal had the trademark to the Frankenstein name.) Beck sold this script to Toho in 1962 where they replaced Frankenstein/Prometheus with Godzilla and the rest is history.
Check out what could have been

"The gigantic octopus is a slimy, loathsome creature and one of Tsuburaya's best creations."
STEVE RYFLE from "Japan's Favourite Mon-Star"