Smallville

Smallville is an American television series developed by writer/producers Alfred Gough and Miles Millar, and was initially broadcast by The WB. After its fifth season, the WB and UPN merged to form The CW, which is the current broadcaster for the show in the United States.[1] The show features a regular cast of characters, which began with eight main characters in its first season. Since then, characters from that first season have left the show, with new main characters having been both written in and out of the series. In addition, Smallville features guest stars each week, as well as recurring guests that take part in mini story arcs that span a portion of a season. Occasionally, the recurring guest storylines will span multiple seasons.
http://en.wikipedia.org/wiki/Characters_of_Smallville