From Bulbapedia, the community-driven Pokémon encyclopedia.
Vladimir the Attacker (Japanese: ジンベイ Jinbei), who is also known as Ralph, is a Pokémon trainer who resides in Lilycove City. His English voice actor is Pete Zarustica.
He appeared in Pokéblock, Stock and Berry and Lessons in Lilycove. Ash, after battling Winona, was eager to teach his Swellow how to use Aerial Ace. However, he wasn't having very good luck with it. Then Vladimir the Attacker approached Ash. An expert on Flying Pokémon, he decided to help teach Ash all about Aerial Ace.
Using his Pidgeotto, Vladimir demonstrated the correct way to use Aerial Ace. He set up a bunch of targets and told Ash he had to try and get Swellow to hit them. Ash had Swellow try this multiple times. Eventually, it got the move down perfectly. Ash thanked Vladimir for all of his help and continued on with his friends to Mossdeep City.
Apparently, Vladimir is very famous as a trainer, since Ash and Max hold him in high respect and even bow down to him.
This is a list of Vladimir's Pokémon in the anime.