Action Comics #248 was something of a milestone in that, while it wasn't the first appearance of the Congorilla, it was the origin of the Bill / Congorilla mind-transfer thingie. Thusly:
As we would learn later in this story, the "hour" time limit is actually a minimum as well. In other words, swap your consciousness with a gorilla and it's going to last an hour, no more and no less. There are rules to this, people!
Anyhoo, Bill gets trapped in a cave (a surprisingly common occurrence in comics) and decides to give it a go:
Well... THAT WAS AWESOME!
And just like that, Congo Bill went from a back-up feature riding on the popularity of Superman to a back-up feature starring a gorilla riding on the popularity of Superman, which (as even the most casual reader of our little fun-house here knows) is bitchin'.
See what I mean? Bitchin'.
Where the gorilla went while Congo Bill was in his human body, I don't know. If it were me, I would want to eyeball the gorilla because... and just bear with me here because this is a perfectly valid point... what if you put your mind into something that died? I presume you have just killed yourself by being careless (which is another fairly common occurrence in comics).
Comic book nerdlingers know that this never happened. Congo Bill's mind was in the body of the Congorilla when Bill's body died, trapping him in the gorilla's body forever.
Which... to be fair... is also bitchin'. Because it's not like anyone cares about Bill when his mind isn't in the body of a gorilla.
Meanwhile, in a totally different story:
Say it with me, Futurama fans!
And... by a good 65 years... Comics Did it First! (tm!)
See you tomorrow!