Ash's Pikachu is a -type Pokémon owned by Ash. He is the first Pokémon Ash ever had and is always by Ash's side. He is also a constant target for Team Rocket. They often try to capture him, but, on the few occasions that they do, their plans are thwarted by Ash and his friends.
Pikachu was Ash's Starter Pokémon, given to him by Professor Oak. Ash showed up late to pick his first Pokémon so he got stuck with Pikachu. Though he didn't like Ash at first, Ash demonstrated willingness to sacrifice himself for Pikachu, and they quickly became friends. Pikachu, who is rather independent in general, believes that he is strong enough without evolving and refuses to evolve into a Raichu even when he was easily beaten by Lt. Surge's Raichu. Later in Ash's adventure in the Sinnoh region, Pikachu was given another chance to evolve after being seriously injured by another Raichu but once again he refused.
Early in the series, Pikachu was given an operation to increase the strength of the electric sacs in his cheeks in order to beat the first Gym Leader, Brock. Despite of this, Pikachu can also get a cold and go out of control when he cannot release his electricity. Most notably, exposure to a magnetic field will cause Pikachu to get a cold. This has been done to him three times in the series, two times by Team Rocket and one time by Zekrom: the first time, Pikachu was cured when the extra electricity was used in attacks against a group of Grimer and Muk, and in the second time was inadvertently cured by one of Team Rocket's battery robots, which subsequently overloaded and exploded. The last time is when Professor Juniper heals him after Ash's battle with Trip in Unova.
Many of the Pokémon animated shorts with all-Pokémon dialogue have featured Pikachu as the main character, and as the main voice of reason. As such, Pikachu is often a leader, helping to break up conflicts among other Pokémon.
Pikachu is one of Ash's most powerful Pokémon being able to defeat pseudo-legendary Pokémon such as Metagross and Dragonite and even actual legendary Pokémon such as Regice. He was also capable of fighting Tobias' powerful Latios to a draw, despite the fact that Electric type moves are not very effective against Dragon types. He also fought Norman's Vigoroth to a draw (during the rematch). Pikachu was used in many of Ash's Gym Battle Frontier and League battles, being able to defeat Juan's Milotic, Lt. Surge's Raichu (although this was during their rematch), Clair's Gyarados, Crasher Wake's Gyarados, Volkner's Electivire, Roxanne's Nosepass and her Geodude, Brock's Geodude and Onix, Roark's Onix, Brandon's Regice, Roxie's Garbodor, Trip's Serperior, and countless other opponents.
However there are times when Pikachu gets beaten fairly easily. For example he was easily defeated by Lt. Surge's Raichu during their first battle, was no match for Sabrina's Kadabra, got knocked out by a single Night Shade from Morty's Gastly, which was Morty's weakest Pokémon, was overwhelmed by Fantina's Drifblim despite his type advantage, lost against Norman's Vigoroth in their first battle, landing only one blow in the process and was defeated in many other battles during his journey with Ash. Despite these defeats Pikachu was considered to be one of Ash's most powerful Pokémon, alongside Charizard, Sceptile, Infernape, and Snorlax.
Pikachu's high level of electrical power has even allowed him to defeat Ground types more than once by using Electric attacks, which normally would do no damage at all. This is notably impossible in the games, where Ground-types take no damage from Electric-type moves under any circumstances, no matter how powerful they are. Whilst travelling through Hoenn, Pikachu learned how to use Iron Tail, which has become one of his signature moves, granting him a technique that will hurt a Ground-type normally, especially if they are also part Rock-type, as many Ground-types are.
In BW020: Dancing With the Ducklett Trio!, a group of Ducklett dropped an umbrella on Pikachu as he was about to use Thunderbolt, which affected his electric attacks as a result. Soon after, Pikachu learned Electro Ball and defeated the Ducklett with this move. He then battled the Sunglasses Sandile. During the battle, Sandile evolved into Krokorok and fired a Stone Edge at Pikachu, who used Electro Ball and sent the move back at Krokorok, blasting it off in the process.
In BW044: The Club Battle Finale: A Heroes Outcome!, he was used to battle Iris' Excadrill during the final round in the Don Battle Tournament at Nimbasa City. Because of a weakness to Ground-types, he was unable to defeat the Subterranean Pokémon and lost.
In BW052: Dazzling the Nimbasa Gym!, he was used in Ash's fourth Gym Battle against Elesa's Emolga (however, he had to use Thunderbolt on Ash beforehand to get his attention to use him, in frustration, as Ash did not even reconsider using Pikachu just once). For this matter, Ash lets Pikachu back in the battle and become friends once again as he leaves all of his plans behind him. Pikachu countered Emolga's Electro Ball with his own and defeated it with Quick Attack. Against her Tynamo, Pikachu suffered many direct hits of Tackle, due to Tynamo's amazing speed, until Ash commanded him to use Thunderbolt to alter the battlefield (this way Tynamo would be forced to Tackle Pikachu head on only). Ash's tactics work and Pikachu used a powerful Iron Tail to land a direct hit on Tynamo as it crashed onto the wall as a result to be knocked out, earning Ash the Bolt Badge.
In BW067: Battling the Bully!, the Sunglasses Krokorok returns to confront Pikachu to a battle (after he followed them all the way from Nimbasa Town, Nimbasa City, Driftveil City, and Chargestone Cave). However, this battle caused them to get blown away in separate directions after the interception of Pikachu's Electro Ball and Krokorok's Stone Edge. However he was found by a boy named Mick who was mistaking him as a pre-evolved form of Zekrom as he show him to his friends Glen and Shaun (who eventually knows this Pokémon from the Kanto region he went to). Now that Mick doesn't know how to battle with Pikachu, he goes away for a while to ask Pikachu some questions alone but was found by Ash and co. including Krokorok. Although Mick persuades Ash to let him borrow his Pikachu so he could battle with Glen and Shaun when Glen says the word "Let's Battle." Since Ash won't leave a kid like Mick in trouble like this, he agrees to as they do some training while Ash use Krokorok as an example for Mick to learn about type advantage and type disadvantage with Pikachu. However Pikachu's move of Iron Tail that Mick used cause Krokorok to lose his sunglasses but eventually found it and puts back on and gets angered to get him to pay Pikachu back but stopped by Ash. After training, Glen found Mick with Ash's friends as Mick put this Pokémon battle to a test with Pikachu but in one condition: this battle requires a double battle as Krokorok teams up with Pikachu just to help him out to battle Scolipede and Seismitoad and win this by brains and skills. Pikachu's teamwork with Krokorok was great as Glen learns his lesson that winning isn't for everything and make it up to Shaun and Mick once more. But then there's a score to settle when Krokorok wanted to has this battle with Pikachu as Ash agrees him to and made a type disadvantage to a win as a result to defeat Krokorok. In the end, the Sunglasses Krokorok felt bad when he lost to Pikachu. Which Ash made the decision to let Krokorok come with him and Pikachu making him his sidekick and a friend indeed.
In BW070: An Amazing Aerial Battle!, Pikachu was used in a Gym Battle against Skyla's Unfezant and defeated it with Electro Ball. He stayed in the battle to fight Skyla's last Pokémon, Swanna. Pikachu's Thunderbolt and Electro Ball were blocked by Swanna's Aqua Ring, defending against the type advantage Pikachu held over it. However, using the hoops that Skyla had used in her pre-battle show, Pikachu was able to jump with Quick Attack to hit Swanna. Eventually, Swanna was able to hit Pikachu with a powerful combination Hurricane and a brutal Brave Bird, after which Ash deemed Pikachu unable to battle, although he didn't faint and he tried to continue.
In BW086: Rocking the Virbank Gym! (Part 2), Pikachu was the final Pokémon to go up against Garbodor. It was going to use DoubleSlap but Pikachu evades it and hits with Quick Attack and then Thunderbolt. When Pikachu tried to use Iron Tail, Garbodor swung its arms upwards, repelling Pikachu and untying the arms. After Pikachu dodges Gunk Shot twice, Garbodor grabbed him and used DoubleSlap hitting Pikachu repeatedly. After this, Garbodor fired another Gunk Shot, this time it hits and also poisoned Pikachu. To Ash's luck, Pikachu's Static ability got activated and paralyzed Garbodor after making physical contact with Pikachu. Despite still being able to withstand a Thunderbolt, the Trash Heap Pokémon was unable to take a hit from the following Electro Ball, and was knocked out, making Ash the winner and earning him his eighth and final Unova Badge, the Toxic Badge.
Pikachu is voiced by Ikue Ōtani in all versions of the anime, except in early episodes of the English-dubbed series, in which Rachael Lillis provided the voice in cases where another character's voice overlaps his. A running gag is how he burns all of main female character's bike with Thunderbolt, which, in turn results in that girl following Ash, except for Iris following Ash after she and Ash bumped into each other. Pikachu also has a fondness for ketchup, which is seen multiple times in the anime.