CLAMP is the four-woman manga group responsible for creating this monster known as Tsubasa: RESERVoir CHRoNiCLE. Incredibly prolific, they've also created a lot of manga that's become quite popular not only in Japan, but worldwide. Some of their other works include X, Card Captor Sakura, Magic Knight Rayearth, Chobits, and Tokyo Babylon. Tsubasa and xxxHolic are their most recent series, both still running in serializations in Japan.

2004 marked a milestone for the ladies, marking their 15th year as professional manga-ka. With this anniversary, they decided to do something wacky -- like change their pen names. So, without further ado, here's CLAMP!

Ohkawa Ageha
formerly known as Nanase Ohkawa
Birthday: 05/02
Blood Type: A
Birthplace: Osaka

Mokona
formerly known as Mokona Apapa
Birthday: 06/16
Blood Type: A
Birthplace: Kyoto

Nekoi Tsubaki
formerly known as Mick Nekoi
Birthday: 01/21
Blood Type: O
Birthplace: Kyoto

Igarashi Satsuki
formerly known as Satsuki Igarashi
Birthday: 02/08
Blood Type: A
Birthplace: Shiga Prefecture

References:

CLAMP no Kiseki volume 1 (Kodansha, 2004, ISBN 4-06-367071-6)
CLAMP no Kiseki volume 1 (Tokyopop, 2005)
FrAU (September 2004, No. 322)