Throughout the Pokemon games, players compete against their rivals, who they are able to name. The most popular suggested name for the rival in the original installments is Blue, who is an actual character in the manga, Pokemon Adventures.
Like his video game counterpart, he is from Pallet Town and is sent by his grandfather, Professor Oak, to go on a quest to catch many Pokemon, hoping that he'll become one of the best trainers out there and that he can complete the Pokedex. Though he has a lot of Pokemon, he didn't catch all of the ones that joined him in his journey, and it may be hard to remember which ones he actually caught, especially since most of them aren't actually shown. Here are all of the Pokemon Blue caught in the first arc of the series.
6 Golduck
Towards the end of the second volume, Blue and Red learned that they needed to go to Saffron City to fight Team Rocket. When they got there in the beginning of the third volume, they found a barrier surrounding the city. To get through it, Blue used his Golduck to use confusion so he could find out what was going on in there. Meanwhile, Red had Pikachu use substitute so its clone could get inside of the barrier. By teaming up, they were able to get through. This marked the beginning of the two trainers having more of a friendship than a rivalry, and it wouldn't have happened without Golduck.
5 Scyther
One of Blue's greatest enemies in the first arc is Koga, a member of Team Rocket and the gym leader of Fuchsia City. When Blue teamed up with Red to fight Koga, as well as Sabrina and Lt. Surge, at Saffron City, the two Pallet Town trainers were split up. Blue fought Koga while Red battled against Lt. Surge. In his battle, Blue had his Scyther attack Koga directly. However, Koga's Grimer was able to trap both Scyther and Blue. Not being able to do anything, Koga told Blue that Team Rocket captured Professor Oak, who refused to help them, and asked Blue if he would get his grandfather to cooperate. When Blue refused to do so, Scyther broke free and tried to attack Koga but failed. Luckily, Red won his battle with Lt. Surge and was able to assist Blue in defeating the Team Rocket member.
4 Pidgeot
Like Scyther, Pidgeot also attacked Koga in Saffron City. When Red joined the battle, Grimer got off of Blue, allowing him to use Pidgeot. However, Blue quickly had it return to its Poke Ball, not realizing that Koga would send out Articuno to attack him and Red afterwards, before they defeated him.
Pidgeot was also seen when Blue competed in the Pokemon League. He used his Pidgeot in the battle that earned him his place in the semi-finals. Unfortunately, this battle wasn't shown but since Pidgeot is seen with Blue before and after the battle begins, it was probably an easy victory in which Blue didn't have to switch his Pokemon. Because of this, it's strange that he doesn't use Pidgeot in more of his fights.
3 Machoke
After an encounter with Red, Blue's Pokemon accidentally got swapped with his. One of the Pokemon that Red received was Machoke, who, like its trainer, did not get along with Red. However, when the two trainers found each other again, they fought a Ninetails, with Machoke being the main Pokemon in the battle.
When Ninetails hurt Machoke, Blue's Pokemon evolved into a Machamp and was able to win the fight. Once Blue and Red returned their Pokemon to each other, Machamp's true trainer thought that spending time with Red was partially responsible for the evolution. Ironically, when they fought each other in the finals of the Pokemon League, Blue used Machamp to fight Red's Snorlax. During the battle, Blue finally thanked Red for helping Machoke level up, showing appreciation while taunting his friend at the same time.
2 Ninetails
The same Ninetails that fought Machamp was also caught by Blue. Not only were their Pokemon accidentally switched, but they also obtained the other's items and Pokedexes. One of the items that Red had was a Poke Ball, which Blue used to catch Ninetails. Because of this, the two rivals fought over who should keep the Pokemon, with Blue forcing it out of Red's hand. However, as he was the one to throw the Poke Ball and it was his Machamp that participated in the battle, many readers agree that Blue was the rightful trainer, though some may argue that Ninetails should have been one of Red's Pokemon. Like Pidgeot and Machamp, Ninetails also helped Blue in the Pokemon League. It fought against Red's Poliwrath and Pikachu, both of which it defeated, before being sent back into its Poke Ball to be replaced with Charizard. However, this was all part of Red's plan as due to combining Poliwrath's water, Pikachu's electricity, and Venusaur's vine, he was able to create a lightning rod which he used to win the fight. Blue may be a great trainer, but he didn't see that coming.
1 Venomoth
Despite never making an appearance, Blue's Venomoth was one of the first pokemon mentioned in the series. While waiting for an opportunity to catch a Kangaskhan in Viridian Forest, Blue fought against weaker Pokemon, hoping to find others that he'd want to capture. One Pokemon that he found was a Venomoth. However, since he already had one, he decides not to catch another. This may also subtly hint that he tries to get one of every Pokemon that he encounters and may have caught a lot more that readers just don't know about.