%20from%2030%20Smallville%20Stars%20and%20Guest%20Stars%20You%20Might%20Have%20Forgotten%20About%20on%20E!%20Online)
Tori Spelling (Seasons 6 and 8)
The former Beverly Hills, 90210 star played the Daily Planet's gossip queen, who had the ability to transform herself into water. She used that ability to spy on people by hiding in fountains and gutters.
%20from%2030%20Smallville%20Stars%20and%20Guest%20Stars%20You%20Might%20Have%20Forgotten%20About%20on%20E!%20Online)
Lucas Grabeel (Seasons 6 and 10)
The High School Musical star played young Lex Luthor and a hybrid Kryptonian/human made of a mix of Lex and Clark's DNA. Sometimes he went by Alexander and sometimes he was Conner, and then he was Superboy, but he was always a little bit confusing.
%20from%2030%20Smallville%20Stars%20and%20Guest%20Stars%20You%20Might%20Have%20Forgotten%20About%20on%20E!%20Online)
Justin Hartley (Seasons 6-10)
Before Stephen Amell, there was Justin Hartley as Oliver Queen. We couldn't have forgotten about him since he was a major star of the show for the second half of its run, but we just love This Is Us so much that we wanted to mention him.
%20from%2030%20Smallville%20Stars%20and%20Guest%20Stars%20You%20Might%20Have%20Forgotten%20About%20on%20E!%20Online)
Brett Dier (Season 7)
Pretty Little Liars and Jane the Virgin star Brett Dier played an alternate Clark Kent, who only existed in an alternate universe Clark once visited, and thought was way better than his own world.
%20from%2030%20Smallville%20Stars%20and%20Guest%20Stars%20You%20Might%20Have%20Forgotten%20About%20on%20E!%20Online)
Christina Milian (Season 7)
Christina Milian played a movie star who was charmed by Clark after he saved her life during a stunt gone bad.
%20from%2030%20Smallville%20Stars%20and%20Guest%20Stars%20You%20Might%20Have%20Forgotten%20About%20on%20E!%20Online)
Richard Harmon (Season 8)
The 100 star dazzled as a teen addict laying on the ground in one episode of season eight.
%20from%2030%20Smallville%20Stars%20and%20Guest%20Stars%20You%20Might%20Have%20Forgotten%20About%20on%20E!%20Online)
Brian Austin Green (Season 9)
Brian Austin Green played John Corben, AKA Metallo, a reporter at the Daily Planet who held a serious grudge against Superman (then known as the Red-Blue Blur) over the death of his sister. He had a heart made of Kryptonite, but that didn't stop him from falling in love with Lois. Too bad he didn't know Lois was destined for somebody else...
PHOTOS: Renewed or Canceled? Find out the fate of your favorite shows