Rey’s Father: Born of a Failed attempt by the Emperor to Clone Himself

Star Wars: The Rise of Skywalker originally featured a line confirming that the evil Emperor Palpatine was in fact a clone of the series’ original villain, according to actor Ian McDiarmid.

Kylo Ren says ‘You’re a clone.’ 

And the emperor said in that original script, ‘More than a clone. Less than a man.’ 

But it turns out Palpatine wasn’t the only clone kicking around, because Rey’s father was born of a failed attempt by the Emperor to clone a new vessel for himself.
After Palpatine’s apparent death in “Return of the Jedi,” he “thrust his consciousness” into a clone body but “the transfer was imperfect.” The Sith Eternal worked hard to produce a better vessel for Palpatine’s consciousness, but not all of these host bodies were successful.

One of the failed hosts was “useless” and “powerless” and “a not-quite-idenitcal clone” of the Sith Lord.
The clone body was not strong enough to host Palpatine. That failed clone would go on to father Rey.

“Dark Empire” even includes a secret Sith world that Palpatine kept in reserve.
Seemingly cut off from the rest of the empire: in the comic it’s called Byss, while in the film it’s Exegol.
Even his Final Order fleet, with its planet-destroying laser cannons, recalls a star destroyer in
“Dark Empire” that also has a superlaser — though one that can just destroy a planet’s surface, rather than the whole celestial body. That ship was called the Eclipse.
And it should be noted that Palpatine tried to transfer his soul into Leia’s unborn son, much as he tried to do with Rey.

And in his final defeat, in the comic titled “Empire’s End” all the Jedi that have ever been agree to keep Palpatine’s soul trapped in the Netherworld of the Force forever, so that he can return no more.

At the end of “The Rise of Skywalker” Rey says, in defeating the clone of her grandfather, “And I am all of the Jedi.”