Ash's Krookodile (Japanese: サトシのワルビアルSatoshi's Waruvial) is the ninth Pokémon obtained by Ash in the Unova region. Prior to its capture, it was also known as the Sunglasses Sandile (Japanese: サングラスのメグロコSunglasses Meguroco) and Sunglasses Krokorok (Japanese: サングラスのワルビルSunglasses Waruvile).
Krookodile made his first appearance in A Sandile Gusher of Change! as a Sandile, where he was revealed to be the leader of a group of Sandile who lived near a local spa resort. He and the group caused trouble at the spa resort on Route 1 so that they could get the attention of the owners. He was actually trying to save the other Pokémon in the area because he knew that a geyser would soon erupt. With the help of Ash, Iris, and the son of the spa resort owner, Dan, Sandile was able to save the Pokémon. In the end, Sandile was shown to have gained respect for Ash, and as such, began to follow him.
Sandile reappeared in Dancing With the Ducklett Trio!, separating Ash from the group in order to battle Pikachu again. However, a wild Ducklett stole his sunglasses and stopped the battle. Sandile was deeply saddened without his sunglasses, losing his usual confidence and becoming quite cowardly. With Ash and Pikachu's help, he defeated the Ducklett and reclaimed his sunglasses. Later, after being healed at the Pokémon Center, Sandile finally got the battle he wanted with Pikachu. Sandile dominated the battle to start with and eventually evolved into Krokorok. Pikachu soon gained the upper hand however, and sent Krokorok blasting off when his Electro Ball attack collided with Krokorok's Stone Edge, causing the stones to hit Krokorok and send him flying.
After a long absence, Krookodile, still as a Krokorok, returned at the end of Explorers of the Hero's Ruin! with the same goal of defeating Pikachu in battle. In the following episode, he battled against Pikachu, and ended up causing the two of them to go flying. He was later found by Ash, and helped them locate Pikachu. It was revealed that Krokorok had followed them through various locations, including Nimbasa Town and Nimbasa City, in order to have a rematch with Pikachu. He also followed them through Chargestone Cave, where he was shown to be the cause of a pen being stuck in the Klinklang in Evolution Exchange Excitement!. Krokorok later allowed Ash to use him to help Mick learn to battle, and he eventually teamed up with Pikachu under Mick's command in a Double Battle against Sean's father's Seismitoad and Scolipede, where the duo eventually won. Krokorok then got the chance to battle Pikachu like he had wanted for so long, and after a hard-fought battle, Pikachu emerged victorious. Krokorok was depressed by the loss and begun to leave, when Ash invited him to join their team. Krokorok happily agreed, and was caught by Ash in a Poké Ball.