Eriol is introduced as a transfer student from England, in Sakura's class. He and Sakura immediately become friends much to Syaoran's dismay. Eriol also makes friends with Yamazaki, following up on his crazy stories and confirming his weird theories. Eriol lives in a huge house with his two other companions Nakuru and Spinel. Even though he seems like this sweet innocent kid who is good at sports, art, cooking, playing the piano and even sewing, he is actually on the scene to cause Sakura trouble. It turns out he is the mastermind of the second arc.

In the manga Eriol is the first half of the reincarnation of Clow Reed. He had 2 missions. The first was to help Sakura change the Clow cards into Sakura Cards, using her own magic, by creating troublesome situations in where she would be forced to do it unknowingly. The second was to help her grow strong enough to split his power between himself and, the second half of Clow's reincarnation, Fujitaka.

When Clow died he was reborn into two people, being Eriol and Sakura's father Fujitaka, but Eriol possessed all of Clow's power and this did not make him happy. His wish was to not be the most powerful sorcerer in the world. So he chose Sakura as his succesor, and sought to split his powers. Only someone stronger than him could do it. However Eriol is not Clow himself, he possesses his memories and power but he is not the exact same thing, as he explained to Yue.

Having Clow's power, Eriol is actually alot older than he looks. He stopped his growth and kept the body of a 10 year old for the sole purpose of meeting Sakura one day. This explains why he is more 'adult-like' and mature, his emotions had plenty of time to develope.

In the anime Eriol's only purpose is to help Sakura change the cards. He is the sole reincarnation of Clow Reed and does not split his power. He is also introduced as a transfer student and comes to bad terms with Syaoran by smiling at Sakura in front of him. He also occupied Meiling's old seat next to him. The rest of the story pretty much follows the manga, only the anime is more subtle about certain things.

Yes, people, unfortunately in the both the anime and manga, it seems Kaho is the object of his affections in the end. Although the anime is once again more vague on the subject.

If you want to know more in-depth tidbits about Eriol, go to the "Etc" section, especially if you are looking for the american Card Captors version of Eriol.