I'm not really up to this, but hey? I do my best work at 2:45 am! Let's just see if that applies to character writing as well, eh?
Let me make a start of it...
Tyrus is a strong man not given to fits of rage or wild insanity. He's of a mind that things can be solved with force, and a fair judgement. He is a strong tactician, but not overly given to subtlety prefering to strike hard in the center rather than split his forces around and flank. (though the flanking manuver would save more lives, and so save more force for later battles, also it will serve to demoralize the enemy as well as increase reknown for the war leader. A subtle hand in battle is everywhere, but a strong blow lands only once. So says Kydran who is the sublte one here) Tyrus is fiercely loyal to his people (whoever they maybe more later) and will fight with all he has to see right done. He beleives that a decisive victory is the only true victory, and cannot stand a defensive posture for long. All this is true of him before Tarikun, most of it is true afterwards, only bent certain ways.
Here is the way of it: Both sides lost at Tarikun, both sides were wiped out for the most part. Tarikun was no decisive victory for anyone, and so it was a clear defeat for both. BOTH sides failed, thus Tyrus failed. Not knowing completely what happened he, being the honour bound leader of the heavy hand, felt it his supreme dishonor to fail his army, and also not to see then along their journey to Valhala or whatever dead warrior Proteans go home to. It has been many years since that day, and he has had many dark nights to stew over it, and turn it over inside of his soul. He has witnessed the decline of his civilization, and also the failing of the rulership to fix things he thinks are needed. This government he has sworn to protect as his people. (they ARE his people!) But he feels betrayed, indeed he sees betrayal behind every door since the Fates (or whatever) betrayed him at Tarikun. He's decided then, after years of torment, that he must create his own world free of such things, and he must create his own race to be loyal to. (since he can't find it in his honor bound military life to be loyal to himself) So he let's in the Antareans. So he steals the Epsilon, so he learns what destroyed Tarikun, and gathers that power for himself. (the Antarean language, and ore combined) So he seeks to remake Io into his own perfect world as a start, since it is a microcosm of the world at large. In Ko he sees a kindred spirit who was also betrayed by Life. He sees the first of his new leaders, and one who shares a similar flaw, but of course Tyrus wouldn't call it a flaw.
This is all stuff that be related either by actions, or by subtle dialogue here and there. In the scene before the Protean King for example if he's there. He can relate some to Ko, and of course the obligatory lecture before the boss fight is just the place for him to rattle off. Now it would be obvious to the player (or anyone with a wit of psychological understanding..let's not make too obvious. No need for him to self analyze!) what his fatal flaw is in his telling of the story. We'd get Kydran's side of it later, and so make a sort of Yin and Yang comparision of affected minds after such a hugely traumatic event.
ah! Now that was a nice brain dump! I feel much better! :p