I see your c!Ranboo theories and c!Connor theories, and I raise you: it was actually c!Schlatt. Here is my evidence.

DreamXD said he got rid of the first time traveler. And what happened to Schlatt? He perma-died after only two canon deaths, the second of which was an unexplained heart attack, which as they said at the time, just isn’t part of the game.

Near the end of his life (and other instances like the rally), Schlatt was shown to be both erratic and confused, like he couldn’t quite remember who/where he was or what was going on. 

Schlatt had the revive book, an item we know came from DreamXD.

Schlatt’s inexplicable friendship with Connor, who joined after Schlatt died, could be explained by them meeting during one or more of Schlatt’s travels through time, as Connor also appears in multiple of Karl’s travels.

Ranboo being the first time traveler does not explain his half-enderman nature because if he is actually black and white because of the Inbetween and Otherside, where does the enderman part come in? Are endermen linked to the Otherside somehow? It doesn’t add up for me

Ranboo being the first time traveler also doesn’t make sense for his connection to Dream. It’s already been made clear in Foolish’s lore streams that Dream and DreamXD are separate entities; DreamXD only looks like Dream because he took on the appearance of the first mortal he saw.

Now that we’ve been introduced to the concept of demigods, it would make more sense for Connor to be another demigod, always showing up in unexpected places with little explanation, than to be the first time traveler who supposedly lost their memory.

Both Ranboo and Connor are still around (ish). Back to my first point, DreamXD said he got rid of the first time traveler.

But I with Jack's character on the Other Side would have kinda just-

"Jack": You're forgetting your friends, and you don't even realize it.

Karl: I could never forget my friends lol.

"Jack": But you are though.

Karl, counting on his fingers: Nooooooo, I've got Sapnaaaaap, I've got Geooorgeee, Tina just moved iiiiiiin, I've... I've uh...

"Jack": Remember when Sapnap and Quackity were trying to convince you that Q was also your fiancee?

Karl: Yeah?

"Jack": That's because he is.

Karl: ??? No he isn't. Fucker killed me lmfao.

"Jack": Then why are there two rings on that finger?"

Karl, looking down at the finger he stopped counting at: ...

Karl: ...Sapnap gave me two of 'em-