Brenner was born to a general who fought against General Forsythe in the Lazurian Siege, which occured 20 years before the meteor shower. In the Siege, the two sides agreed to a truce to bury the casualties. The father ended up dying in battle and losing the war at the same time, which brought on a wave of criticism from the government he worked for, while Forsythe and others praised him. It was probably the father's sense of good which transferred to Brenner and created him into the man he was in the game.
In Days of Ruin
20 years after the Siege, the infamous meteor shower arrived, killing 90% of the population and creating a frantic power struggle between the remaining remnants of the Lazurian and Rubinelle armies. Brenner survived the catastrophe, and created Brenner's Wolves, an army that he controls and his goal is to save the survivors in need of help. Among the notable people who worked for him is Lin, the calm second-in-command who is much more merciless and cruel, and doesn't exactly share the same compassion for people as Brenner did.
One day, while dong some scouting, he saw a boy in trouble from a group of bandits led by "The Beast", an ex-soldier who has a hot temper. Brenner and Lin drove off the group and rescued the boy. The boy was Will, the main protagonist of the game, and Brenner became his mentor, instilling his values of human goodness and peace during their adventures. They would eventually meet Isabella, who would befriend and help Will and the army, and Dr. Morris, who would become the main and key medic of the army.
After saving pilot Waylon against a Lazurian army, Brenner discovered from Waylon that there was the New Rubinelle Army led by Brenner's ex-boss Greyfield. Deciding to end the feud between the Lazurian and Rubinelle forces, Brenner's Wolves joins Greyfield and his group. But after they finally defeated the Rubinelle forces, Brenner decided to defect against Greyfield and free the Rubinelle prisoners of wars due to his disgust in Greyfield and his cruel execution of Forsythe, the head of the Rubinelle Army (who Brenner's father fought against). He and others held off the pursuit army so the prisoners can escape, but it was his last battle. Wounded several times, he was finished by Greyfield's big weapon created by Caulder, destroying him and the other Lazurian troops in the area.
Brenner's death was a huge shock to Will and the prisoners. But after he was gone, Will took over as Brenner's Wolves, and it was the constant lessons and tutelage from Brenner which helped him to defeat Greyfield and eventually Caulder and the IDS (Independent Defense Systems)
In a time when world order collapses and anarchy arises, Brenner was the exception rather than the rule. Like Forsythe and presumably his father, he values peace and rules that bind the world and people together. He also believes in the goodness of human beings and could even be considered too lenient. For example, Brenner agreed to help a corrupt leader of a group of survivors even though Lin clearly knew that the leader is hogging all the food for himself. However, Brenner defends his beliefs with great zest, which leads to conflicts with people who have extreme opposite beliefs, such as Greyfield and Waylon.
Brenner is also a leader. His subordinates follow him whereever he goes. Sure, Lin could argue and bicker with his beliefs and a friendly, non-violent fashion, but even so she, WIll and people who sided with Brenner's Wolves respects him deeply and knows what he stands for.
As a CO
Brenner emphasizes defense, which reflects his defense of life and human decency. He doesn't have a favorite type of vehicle (aerial, ground, naval) but when he boards a unit, the attack and defense of the unit increases (defense increases more), and all units around the boarded unit also has a minor defensive boost. If the CO gauge is full, Brenner can unleash Lifeline, which heals all his units by 3 HP.