Ur-Didact. Well, he didn't exactly get a say on the release sequence considering that he was knocked out and dragged into his Combat Cryptum by the Librarian. As for the blue Prometheans, they were under the control of Endurance, who was convinced by the Librarian to defend the Didact from any intruders, so he was not released early. Obviously, the Didact was not ready, which is why they were attempting to repel the Chief. And why the Knight didn't immediately execute the Chief after pouncing on him.