He teamed up with Ash to get the Pokémon back which were stolen. He was then forced to battle Ash in the Indigo League and defeated him, as Ash's Charizard wouldn't obey him. He battled Assunta for the next round, but lost. He went to Ash to have few words about their loss and defeated Team Rocket, who wanted to take their Pikachu away.
In Pokémon Diamond and Pearl, during the contests, there is a contestant named Luis. He seems to be based on Ritchie because of his outfit and having a Pikachu nicknamed Sparky.
Ritchie mentioned in Oaknapped! that he and Ash tend to catch the same Pokémon.
Ritchie deisgn is similar to Red from Generation I, he is a pallette anime swap for Red, the differents Red clothes are Red & White Jacket, Shoes, and Hat, while having blue pants, Ritchie has Blue & Yellow Hat, Green Jacket, Pants, possibly Blue, Green, or Purple Shoes, the point this that he wear the outfit as Red do in Generation I not Generation III on Generation I.
In Friend and Foe Alike, Ritchie battled Assunta, though it was not specified whose Tentacool and Spearow were.