3. Prometheus
Prometheus is little-known to those who are simply fans of Batman through The Dark Knight trilogy or earlier live action films, but would actually have been a very important villain for Bruce to have faced throughout the series, as he is effectively Batman's dark shadow, a reflection of what Bruce's life could have been. He was the son of two criminals who eventually gave their lives to protect Prometheus from the police, who gunned them down right in front of him, turning Prometheus's hair white through shock. Whereas when Bruce's parents were killed he took up the fight for good against evil, Prometheus went the other way, swearing an oath to "annihilate the forces of justice". The comparisons with Bruce Wayne don't stop there, Prometheus too had an extremely large amount of money left over from his parents, as well as from extorting local mob bosses. However, he soon left his home in order to travel and train himself in all of the skills he would need to accomplish his plans, training in various countries as well as joining terrorist cells in the Middle East. His travelling and training in various countries also mimic Bruce's travels, thus enforcing the role of Prometheus as the villain with the most similarities to Bruce Wayne in the Dark Knight trilogy, which would definitely have marked out a climactic showdown between the two of them if he were to have been included.