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If you mean "Is Juan the leader in Pokemon ruby?", then no. It's Wallace who's the leader. Juan is leader only in Pokemon emerald. The champion is Wallace in Emerald, but Steven is the champion is Ruby and Sapphire.
In the 8th gym. he is the gym leader
He is the sootopolis city gym leader.
Wallace he was the former 8th gym leader in ruby and sapphire
Wallace is the Gym Leader of Sootopolis City so you will be able to verse him once you challenge the Gym.
Juan is a gym leader in Sootlopolis City. To get there, you have to use dive. Wallace will be the champion. In ruby and sapphire, Wallace will be gym leader and Steven will be champion.
In Pokemon Ruby, Wallace is the gym leader of Sootopolis City. When the player first arrives in the city, Wallace is not at the gym. He and Steven are north of the city. They take the player to the Cave of Origin where Groudon is encountered. After this battle, Wallace can be found and battled in the Sootopolis Gym.
Steven in Pokemon emerald is a rock collecter. With his help you also defeat team magma in Mossdeep city. Back in the days of Ruby and Sapphire he used to be the Pokemon champion, but now he is replaced with the former gym leader Wallace.
You need REALLY strong Pokemon the defeat the leader. His minions are easy. The leader has three Pokemon and they are all fire.
I'm sorry to say it, but "that guy" is not a Pokemon. He is, however, the leader of the Sootopolis Gym. In Ruby and Sapphire, he was Wallace. But in Pokemon Emerald, he became Juan. Wallace then became the Elite Four Champion.
If you have Ruby and Sapphire, you can go up the Sky Piller after you defeat Wallace. Otherwise, you have to trade is by trading from Ruby, Sapphire or Emerald.
ground. He is an electric type.