He and Heero have a long time standing knowledge of one another. It is because Heero, as a child of 7 or 8. shot him with a launcher of some sort that Treize was hospitalized and ended up meeting Leia Barton, the mother of Treize's only child, Mariemaia. When he builds a Gundam of his own, Epyon, he gives it to Heero to replace the loss of both Wing and Wing Zero, never telling the teen that the suit is equipped with the dangerous Zero System as well.

The noble and honourable Treize also has some history with Wufei as well. When reports came of a Gundam on the L5 colony cluster, he let it be, never dreaming that he was eventually meet face to face with it's pilot, Chang Wufei. Wufei challenges him to a sword match, and loses, for Treize is not only a figure head but a well-trained soldier of war as well. 

Treize demands elegance and honour from all that follow him, a point that has be told to Une on more than one occasion. He is an excellent marksman, wonderful sword fighter, and a very decent mobile suit pilot. (He trained Noin himself!) A few of the General's quirks are that he has a soft spot for roses and rose-scented baths.

It is because of Treize's honour that he receives such loyalty from his officers when he is trapped in his own home after he disagreed with Romefeller's use of the Mobile Dolls - a mobile suit that disregards the death of human pilots and degrades the act of war altogether. The Treize Faction frees him from his prison and he joins in the final fight of the war, meeting up with his former adversary, Wufei. He loses his life, but does not damn or hate the boy who has killed him and dies in peace - as far as we know.