As the series progresses, recurring guests appear at various times to help move the overall storyline of the show or just provide a side-story arc for one of the main characters, such as Brainiac or Adam Knight.
[35] Pete returns to Smallville in season seven's "Hero", after gaining superhuman abilities from kryptonite-enhanced chewing gum, which allow him to stretch his body to extreme lengths.
[33] Jones was not alone in his wish to get more screen time; the writers, who were reading Internet forums and receiving mail from the audience that requested the same thing, decided that Pete would learn Clark's secret in season two.
The creative team hoped that knowing Clark's secret would allow the character to be written into more scenes, and become involved on a daily basis with the Kent family.
The writers also realized that they could not kill off the character, and so chose to send her to the US Senate, creating a parallel to Clark where Martha fights injustice on the political stage.
He also saw his character as a means to keep the show grounded in reality, specifically by making sure that Jonathan's life is clearly displayed for the audience, by performing a daily routine on the farm.
[63] A heart condition is not new to the character, as it has been used in previous incarnations, like Glenn Ford's portrayal of Jonathan Kent in Richard Donner's Superman, as well as the comic books.
Gough and Millar began to like the idea of bringing in a new character, one that would create a new love triangle; eventually they tied him into the larger storyline involving the three Kryptonian stones of knowledge.
[84] In "Committed", a deranged jeweler kidnaps Jimmy and Chloe after their engagement party and subjects them to a torturous test to see if they truly love each other—they both pass and are allowed to return to their normal lives.
[90] Aaron Ashmore's twin, Shawn, who is better known as Bobby "Iceman" Drake in the X-Men film series, appeared in two episodes of Smallville as the power leeching Eric Summers and had been considered for the part of Jimmy Olsen in Superman Returns.
[101] Unknown to Clark, Brainiac is not killed in their fight on Krypton, and he manages to place Kara in the Phantom Zone, while he assumes her identity back on Earth.
Cassidy Freeman portrays Tess Mercer, the acting CEO of LuthorCorp, who is Lex Luthor's protégé tasked to run the company should something ever happen to him.
That same episode reveals that Tess is bringing together a group of meteor-infected individuals, and in "Plastique" she recruits Bette, a young girl with the power to create combustion and explosion remotely.
[106] In "Toxic", it is revealed that Tess had a prior romantic relationship with Oliver Queen after she saved his life while he was stranded on an island, but broke up bitterly when he cheated on her.
Visibly upset by this, Tess places a jamming device into her necklace to disrupt the signal, but not before telling Lex that she will cut him off from the outside world and sell off everything that he owns.
[114] In the series finale, Tess is killed by the revived Lex Luthor after she administers a neurotoxin that removes all of the clone's memories in an effort to protect Clark's secret identity.
Davis starts to suspect the same thing himself when he begins to lose track of large portions of time, and finds himself covered in blood, but with no wounds on his own body.
[106] Davis is informed by Faora, the wife of General Zod, that after the pair learned they could not have children that he was genetically created to adapt to any injury and to be Earth's ultimate destroyer.
[123] Brian Peterson explained that he, and the rest of the new executive producers, were looking for a villainous character that was "as great as Lex", with Michael Rosenbaum's departure at the end of the seventh season, and Doomsday fit what they were looking for.
Instead Dario Delacio, a stunt double who stands at 6 feet 8 inches (2.03 m), performs the role of "Doomsday" when the creature's monster form appears throughout the season.
[17] In the episode "Solitude", Brainiac attempts to release him from the Phantom Zone where it is revealed that Clark's biological father Jor-El placed Zod's spirit after destroying his physical form.
[130] Season nine episode "Kandor" reveals that the Kandorians are in fact clones created by Jor-El—at the orders of the Kryptonian Council—who also corrupted their DNA to prevent them from having powers and subsequently enslaving Earth.
Swann first meets Clark in the season two episode "Rosetta", where he explains his team of scientists intercepted a message from space and were able to translate it based on a mathematical key which accompanied the transmission.
In this episode, Clark is taken to an alternate reality where Adams, an agent for the Department of Domestic Security, is providing Lois with inside information on President Lex Luthor's operations.
[152] A clone of Jor-El is released on Earth in the episode "Kandor", but he is murdered before he can fully reunite with Clark and is only able to share a single moment with his son before dying.
[154] The refusal by the film department to allow Smallville to cast a body as a physical representation of Jor-El forced the special effects crew to come up with a creative way to display some sort of aid to help the audience visualize this disembodied voice which was supposed to be talking to Jonathan in season three's "Exile".
To save money on this effect, the crew filmed John Schneider on a black backdrop, and Entity FX digitally added the force field around him.
It is revealed Adam was once Chad Nash, a man who died of a rare liver disease, and the injection of a drug given to him by LuthorCorp resurrected him and is the only thing keeping him alive.
[168] The reprogrammed Brainiac returns in the season ten episode "Homecoming" to show Clark his past, present, and future and help him find confidence in becoming the hero the world needs.
Marsters believes his character wants to get rid of the humans because they are doing nothing but destroying their own planet, and Brainiac sees it as his duty to perform "pest control" on the species.