Eusine

Eusine, The Mystifying Trainer, from Celadon City, is a trainer who has been searching for Suicune since his grandfather told him of the Legendary Pokémon.

He is first encountered in the Burned Tower with Morty. Eusine is an old friend of his, according to Morty. He is later battled in Cianwood City after spotting Suicune. After the battle, Suicune is seen in various places along with Eusine. After finding it enough times (scattered throughout some select routes), Suicune finally is seen on Route 14, where Eusine will wonder who would find it first. The last time Eusine will be seen is at Cerulean Cape, where you will get the chance to encounter and battle Suicune (having gotten there before Eusine). Even though Eusine feels envious, he believes Suicune respects the player as a good trainer, as shown by its eagerness to battle the player, so he reluctantly backs down, encouraging the player to battle Suicune.

In the Anime
In the episode For Ho-Oh the Bells Toll!, he comes off as a proud and arrogant person with a slight superiority complex and exhibits a near-religious fervor for Suicune, challenging Ash for daring to say that he'd met the legendary beast. This may just be a form of jealousy on his part, for Ash had also seen Ho-Oh as well, while he has yet to encounter any himself. In the same episode, when he finally saw Suicune, he tried to catch it partially for ego gratification, ironically making him no better than the people whom he had mentioned were unworthy of it. This is somewhat interesting compared to his appearance in The Legend of Thunder! when he mentions Suicune only once, and then only in reference to the other beasts.

Trivia

 * Eusine's clothing somewhat resembles Suicune's design.
 * His trainer class was called Mysticalman in Generation II, while he is called the Mystery Man in the Generation IV remakes.
 * In Legend of Thunder, the English dub refers Eusine as Eugene.