Marvel, I am well versed in the comics as I have been reading them since the late 70's. I am aware that the Brotherhood attacked the White House and Trask's response was the creation of the Sentinel program but I'm also aware that as my definition of antagonist fits Trasks. He views mutants as a threat to humanity eventhough his own son is one. He creates the Sentinels (Master Mold) to capture or kill all mutants. In one of those raids Beast is captured and Trask uses a device to read his mind and realizes that the X-Men who are mutants are here to protect mutants and humans alike. He then sacrifices himself to help the X-Men to stop his creations. The reason I say the big bad can be Bastion is because Nimrod, a time traveling sentinel from the future merges with Master Mold and form Bastion who then resurrects Trask in the future. This is not a cartoon, this is from the book and just an idea of how this could work and I'm not saying this is what they are doing but it could be an avenue they could take.