Ron Damian was none other than Eren Idril in a disguise!
Eren was using Reen fused with his body to take care of the E-Rank wine, lest he suffers side effects. He decided to go with the name Ron Damian because he couldn't find a good name.
But Reen told him to go with anything "random" after feeling his conundrum. So he derived the name "Ron Damian" from the word random itself.
Eren didn't want to but somehow ended up taking a portion of Dom's facial features. He still wasn't used to shapeshifting after all.
Plus, Reen must have shared gene memories of her prey with Eren during their fusion. That's why he could only change into a certain personality Reen had eaten so far. That restricted the number of people he could take the shape of.
But the good thing was that he could tweak his appearance to make it look like he only looked like Dom but wasn't. This was the reason Julie thought Ron looked like Dom but later discarded that idea.
