Michael Hogan, of Battlestar Galactica fame, guest stars on the episode "Patriot." He portrays Colonel Slade.
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Alan Ritchson is seen in this shot from the episode "Patriot." The character makes a major comeback on the final season of Smallville.
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Alan Ritchson returns to Smallville on the episode "Patriot." He reprises the iconic role of Aquaman.
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Why is this photograph significant? Because it's a shot of the video Ella Lane recorded for her daughter.
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Christine Welles appears on the episode "Abandoned." As Granny Goodness she causes problems for Tess.
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Tom Welling is seen here as Clark, courtesy of a scene from the Smallville episode titled "Abandoned."
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Lindsay Hartley makes a significant guest-starring appearance on Harriet on the episode "Abandoned. She causes problems for Clark and Tess.
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Surprise, Clark and Lois! The latter's father stops by for Thanksgiving on the episode "Ambush."
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This is the first photo we've come across of Lindsay Hartley. The actress will play Mad Harriet on the show.
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Erica Durance is seen here as Lois Lane. She's anchored the show for years, of course.
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Los is transformed into the goddess Isis on the aptly-titled episode "Isis." She develops her own powers as a result.
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Oliver Queen takes on his Green Arrow persona in this episode still. It's from the installment "Isis."
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Smallville Quotes

Clark: She saw it.
Nurse: Saw what?
Clark: Her future.

Ryan: (after being kissed by Lana) I don't know, but I'm definitely in love.
Clark: Join the club.