Dexter's Laboratory (1996–2003)
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Dexter's Rival/Dial M for Monkey: Simion/Old Man Dexter 

Boy genius Dexter wants to stay up and watch the 8 o'clock movie with his family, but his mother says he's not old enough. Using one of his inventions makes himself older, but maybe he's made himself a little too old.


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Episode cast overview:
Dexter (voice)
Allison Moore ...
Dee Dee (voice)
Mandark (voice)
Teacher #2 / Principal / Robot / Monkey / Captain (voice)
Dad / TV Announcer / Old Man Dexter (voice)
Mom / Teacher #1 / Computer / Worm (voice)
Main Title Narrator (voice)
Simion (voice)
Robert Ridgely ...
Commander (voice) (as Bob Ridgley)
Honeydew (voice)


In "Dexter's Rival", Dexter clearly shows disdain for a new kid in school, who has a lab just like his, albeit a bigger and more superior one. In "Simion", the result of an failed experiment vows revenge against the humans that did it. In "Old Man Dexter", Dexter makes himself older so he can stay up later. Written by Anonymous

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Release Date:

12 May 1996 (USA)  »

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Did You Know?


In a quiz session, Mandark says that Thomas Jefferson wrote the Bill of Rights. Jefferson was serving as U.S. Ambassador to France at the time. George Mason wrote the Bill of Rights. See more »


Dee Dee: [clock strikes 8] AHHHHHHHHHHH! 8 o' clock! I got the blankets!
Mom: I've got the popcorn!
Dad: And I've got the remote.
[they pile on the couch to watch a movie]
See more »

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User Reviews

Third episode rules, let's Meet "Mandark.
12 May 2009 | by (United Kingdom) – See all my reviews


a. „Rival" – episode introducing Mandark as a new character and the biggest rival of poor Dexter, which is not the smartest kid at school anymore because of his arrival, but not everything is lost, because Mandark falls in love :) with whom? Find out yourself. The first episode in my opinion fully complete with comedy, parody, love and drama. Must see. 5/5.

b. „Simion" – actually the first Monkey episode which is targeting a bit older audience. It is about an invasion on planet Earth of a mad gorilla called Simion which hates earth and human beings, because they treated him extremely bad, so he seeks vengeance. This episode is for a change multi-levelled in meaning, especially in compare to previous 2 monkey stories. Enjoy. 4/5

c. „Old man Dexter" – if the „Rival" was complete, then this episode is an instant classic. Great plot, load of laughs and brilliant dialogue. It is funny what kid (especially if the kid is science genius) can do to watch the Saturday night thrill movie. This episode is so well done, that the normal „must see" recommendation is not enough. Absolute classic. Considering that it is only 6th Dexter's story out – makes you think how many more such cool episodes will come out!!?? Can't wait to see them all. 5/5 Total rating: 9.3/10.

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