B73 was the primary Bastion unit sent to attack Eichenwalde. All of the Bastion bodies found in Eichenwalde are labelled "B73", suggesting that this Bastion led an army of duplicates. He is also a playable skin for Bastion E54 in the 2016 videogame Overwatch.
B73 wanted nothing more than to wipe out the Human race so that the Omnics can own the planet. He is single minded in his goal of wiping out the humans.
B73 and his duplicates were sent to attack Eichenwalde along with larger Omnics, destroyer aircraft and the unique Bastion E54, B73 and his army of duplicates marched through the forest to engage the German army, led by Balderich's Crusaders.
For unknown reasons E54 shut down in the forest, remaining inactive even long after the conflict, only to awaken with sentience years later. B73 and his duplicates fought the Crusaders, with many casualties on both sides, eventually B73 and his duplicates reached the castle and killed Balderich, however they were unsuccessful in the invasion thanks to the valiant efforts of the Crusaders.
B73 and his duplicates remains were left throughout the abandoned castle town and were still there even years later.