Eldes first appears alongside Mr. Verich and Ardos when Ardos saves Michael's sister Jovi from Zook, and is later encountered by Michael when he first visits Mt. Battle. However, he—like Mr. Verich—is shrouded in mystery until the end of the main storyline, where he first battles the player.
As well as being a Cipher Admin, Eldes serves as one of Greevil's two bodyguards, the other being Ardos. At the end of the game, it is revealed that Eldes is one of Greevil's two sons. Eldes eventually stops Greevil and Ardos from blowing up their base, as he realizes that countless people and Pokémon would be killed in the process and this would be immoral.
Eldes is not as evil as the other Cipher Admins. He questions Cipher's motives throughout the game. He also shows regret that when he first battles Michael, he is battling him as an enemy and not in the traditional way, to decide who the better Trainer is.
In Orre Colosseum, Eldes favors using Earthquake alongside Pokémon that are immune to it.
"Mr. Verich tends to his many important business undertakings from Gateon Port. We do a lot of traveling from here. When we get some rare time off, we like to relax and unwind leisurly. I'll ask that you keep it quiet and refrain from disturbing us."
"Well, well? Didn't we meet at Gateon Port? Have you come to train?"
"This is an excellent place for people to train. I've trained here myself."
"Back then, I only sought to be more powerful. I didn't need any other reason. As a result, I attained this status. But now, I've taken to questioning my motive for gaining power. I wonder what I am fighting for. I ponder if I am putting my Pokémon under cruel stress… That's why I urge you to look into yourself. Ask yourself why do you want to become stronger before you take that path."
"You've finally managed to anger Master Greevil. I though I would end up battling you one day… But this isn't how I had hoped to face you."
"If we battle, it will only be unfulfilling and without meaning. Will you challenge me knowing that?"
Yes:"Fine. I understand. But once we begin, expect no mercy. That is my philosophy."
No:"I'm sorry… The Grand Master's orders are absolute. I can't refute them."
Before battle (if lost before)
"If that's what you want, I will accept your challenge. Expect no mercy!'
"We lost. Totally…"
After being defeated
"You are powerful. Much more than I had imagined. If you aim to stop our plan, then you should keep going. However, the Grand Master's power is probably far greater than you can imagine. I doubt you will beat the man…"
After defeating Greevil
"Please wait. You're willing to sacrifice everyone so you can escape? You should be ashamed!"
"Father, you've lost sight of what is important. You got carried away by this whole Grand Master nonsense. It isn't possible to take over the world by producing powerful Pokémon. Just think of this child…"
"This child's pure heart won out over XD001. We were in the wrong."
"Cipher is finished. Father, you yourself should know that more than anyone."
"Now, please. Stand up. This is how it should be. The laws of the land will render judgment on what we have done."
"Thanks to your courage, we were finally able to wake up from our nightmare. Thank you. You'll have nothing to fear from us ever. You should return home to your family. Let us meet again, too. The next time we battle, it won't be as mortal enemies. I will look forward to it."
"Oh, hello! I'm glad to see you again. This time, let's battle fair and square!"
"Fufufu… You really are tough after all. You're worthy of respect."
"I'm satisfied that I was able to battle to my heart's content. I would like to confer on you the title “Eldes's Top Rival.” With your skills, you shouldn't lose against even the best Trainers from around the world. I guarantee it. Let us meet again.