Eriol

Information:
Eriol first appears in episode 36, the first episode of the third season. He is a mysterious magician boy with two winged guardians. We soon see them in their "plain clothes" forms as Eriol, the new transfer student; Ruby Moon, his big sister and Spinel known as Suppi their "cat".

Character:
Eriol is one of those people with whom you can never tell if they are joking or trying to say something deep. He is very respectful of Sakura and offers her flowers and compliments. He also seems to have a particular soft spot for Syaoran who he treats like a younger brother, teasing him constantly in a subtle way. Eriol may seem very proud and aloof at first, he may even seem cruel but that's just his sense of humour and he can't hide the fact that he is wise beyond his years.

Love life and relationships:
This is a complicated issue due to Eriol's particular circumstances! Do not read on if you don't want spoilers.

Eriol is sadly not the one for Tomoyo, their relationship is platonic and they don't spend much time with each other, nor do they seem to care much for each other, both being quite preoccupied with Sakura's love life and adventures.
Eriol is Clow reborn. He is not Clow but has all his memories, powers and knowledge.
It would appear at the end of the series that Eriol is living with Kaho. The explanation for this strange pairing could be that they are reincarnations of Clow and his wife reunited in this life despite the new bodies' age difference. Either that or she is an apprentice and guardian to him.
Eriol is not in love with Sakura, he regards her as his successor and a sort of granddaughter. He is very fond of her and very proud of her accomplishments. He is also very happy that she finds love with his great-great-grandson Syaoran Li.
Eriol is not as close to Yue and Kero as Clow was but he has great respect for them. Eriol is much closer to his own guardians Ruby and Spinel.