Mason Ordrosso in the manga

Chronos Number XII. Mason is the eldest member of the Time Guardians. Although he never participated in a single battle in the series itself, he is the most wise and experienced out of all the Time Guardians. It is explained in the manga that he was the lone survivor the last time the Chronos Numbers fought against Tao-users. He only appears in the final part of the manga, witnessing from afar the explosion of the castle with Belze.

Mason Ordrosso in the anime

In the anime, Mason is radically different because he is later revealed to be working against Chronos in secret. He takes part in the planning the Chrono Numbers' missions from the start of the series, but is not particularly important until the final part of the story, when he reveals that he has been planning a conspiracy against Chronos for 20 years, since the end of the Taoshi War. During the war, Mason turned to the side of the Taoshi and learned the Ultimate Tao Technique from a Sacred Taoshi (though this seems to only be a powerful energy blast). He plans on using Eve to activate Eden to achieve "World peace", which actually involves absorbing all mankind into Eden to fuel it. Mason is the leader of the Zero Numbers, who are comprised of Emilio Lowe, Baldorias S. Fanghini, Kranz Maduke, Shiki, and Kanzaki (Doctor) (The latter two were originally from the Apostles of the Stars). Mason's unnamed Orihalcon weapon appears to be a golden suit of armor that covers every inch of his body except his face, and also includes two large swords. He is possibly the most powerful fighter in the anime series, as he defeated Sephiria and Train easily, and even Creed struggled against him, although during Mason's fights with Creed and Train, he was protected by the power of Eden. It is most likely, but not fully confirmed, that Mason was killed by Creed at the end of the anime.