Shimon, known as Siamun Muran in the Japanese version, was a member of Pharaoh Atem's court, serving as his chief adviser and grand vizier. He was the original wielder of the Millennium Key, though he eventually relinquished his position as a guardian to Shada. Solomon Muto is his modern day counterpart.
Shimon was originally one of Pharaoh Akhenamkhanen's guardians, and he was granted the Millennium Key to hold. His Ka (or his monster spirit) that he summoned was "Exodia the Forbidden One" and after he used Exodia to destroy the force that was attacking the Egyptian capital, he swore to never use it again and sealed the creature away inside five individual stone tablets. He apparently gave up his position as guardian to Shada, and to him he relinquished the Millennium Key.
He plays a largely minor role in the Millennium World arc at first, as he introduces much of the ancient ways and terminology to Pharaoh Atem.
When Zorc Necrophades rises and begins to march on the city, Shimon takes up the Millennium Key that Isis brought back and he summons Exodia to combat Zorc. Although Exodia experiences some success, especially after Siamun demonstrates its ability to regenerate after its arm was torn off by Zorc, Zorc ultimately overpowers Exodia because its power is based on Siamun's, while Zorc can draw power from the darkness. Therefore, Exodia is destroyed and Siamun is killed.
Dark Duel Stories (Duel Monsters III: Tri-Holy God Advent)
Paradox appears in Yu-Gi-Oh! Dark Duel Stories (known in Japan as Yu-Gi-Oh! Duel Monsters III: Tri-Holy God Advent) as an opponent in the third tier set in ancient Egypt. His deck mainly consists of LIGHT-attribute Monsters. His most powerful Monster is Skull Guardian.
Paradox appears in Yu-Gi-Oh! Duel Monsters 4: Battle of Great Duelist as a first tier opponent. This time, he uses all low-level Normal Monsters, including a few previously used by Pegasus J. Crawford (albeit not used to their potential). Paradox's deck also contains the four limbs to Exodia (like Sugoroku Mutou), which he will not play, and cannot be completed without the fifth piece.
His Ka is Exodia, and his present-day self Solomon Muto plays an Exodia Deck in World Championship 2004.
In episode 201 of the English dub, he says the phrase "So let it be written. So let it be done." This was taken from the (for lack of a better term) catchphrase of Pharaoh Ramesses II (played by Yul Brynner) in the epic film The Ten Commandments.