Trueman

Trueman (also known as Mr. T) is a mysterious character that appears in the fourth season of Yu-Gi-Oh! GX. He appears to be pursuing the engmatic student Yusuke Fujiwara. He Duels Jaden and loses, but as he departs, he warns Jaden that the worst is yet to come. He has the ability to transform into darkness (in the form of Duel Monsters cards emanating black smoke), create wormholes and manipulate matter. Stranger still, many of him seem to exist in the alternate dimension he lives in. It is unknown whether they are identical soldiers or clones, or, alternatively, if Mr. T has the power to split himself, as they later merge to duel Jaden. Adding to how strange he is, his physical body appears to be made up of cards and dark energy, and he can disassemble himself at will, such as when Jaden tried having Neos attack him outside of a duel. Despite his repeated defeats by Jaden, he (or they if there's more than one) never give up on trying to get rid off him, and accomplishing whatever it is that he's up to.

After his initial defeat two Trueman are shown in an alternate dimension observing Jaden. They feel that he has become a considerable obstruction to their goals and that he should be eliminated as soon as possible. Jaden duels Trueman a third time (this time in the form of five Truemans merged into one), and defeats him yet again, but Trueman, still alive after the duel, tells Jaden yet again that it isn't over.

Deck
Trueman plays a Darkness Deck, based around "Dark Archetype's" effect to Summon a miscellaneous variety of powerful monsters. Aside from Dark Archtype, he never uses the same card again in a later Duel, implying that he has more than one Deck. As part of his darkness theme, most of his strong monsters are Dark Attribute.