Nascour is a sly, smart member of Cipher, the evil organization in Pokémon Colosseum for the Nintendo GameCube. Throughout the majority of the game, he has all of Orre convinced that he is the leader of Cipher. However, there is some evidence in the game that shows that he is not.
He is a powerful trainer, as is shown in the battle against Wes at Realgam Tower. Other than these times, he is never seen facing off against an opponent, as it seems that he has the Cipher Admins do that for him. Besides Wes, he is the only known trainer to ever beat one of the powerful Cipher Admins, Dakim.
While Nascour is portrayed as relatively nice (albeit a little creepy) when he is first met outside of the Mayor's House in Phenac City, he becomes quite sadistic when you meet him later throughout the game as he finds out that you are trying to thwart Cipher's Shadow Pokémon goal. He takes a harsh tone towards both Wes and Rui, and tries to keep them away from Realgam Tower during its completion by sending off Cipher Peons and other members of Cipher to stop them.
During the game, he is considered to be the leader of the crime syndicate Cipher. However, it is revealed after he is defeated at Realgam Tower that the true leader is Evice, or Es Cade, the mayor of Phenac City. This explains why Nascour left the Mayor's House in the beginning of the game, and Es Cade seemed to be perfectly cheery when Wes entered. It also shows why Es Cade did absolutely nothing in the war against Cipher, and Nascour tried to stop him many times.
He is possibly the third-in-charge of Cipher, as the true master is Greevil. However, this is never confirmed. He just works as a high-ranking lackey (possibly a higher form of a Cipher Admin) to Evice.
Everybody from Cipher in Pokémon Colosseum refers to him as their master. For example, Dakim (after being beaten at Realgam Tower), states that the only people he has ever been defeated by are Wes and Master Nascour. Therefore, it is possible that either the Admins don't know Evice is their master (which is counter-seen when Miror B. is inside the Mayor's House in Phenac), or that he truly is very high up in rank on Cipher.
In battle, Nascour is a powerful opponent. He often uses stat-enhancing items, such as the X Attack and X Defend to give his Pokémon boosts in their abilities, while he has the other one attack. By doing this, he can over-power one or two of his Pokémon and use them to take out your entire team. This is usually avoided by having a type advantage and Speed advantage against his Pokémon. (Psychic and Dark types can be used to win this battle easily. The starter Pokémon for this game, Umbreon and Espeon, can be used to make it much easier.)