Conomor's first wife pulls from the legend of the tyrannical giant Cormoran who is loosely based on Conomor, specifically Cormoran's wife Cormelian. In some versions Cormelian was Conomor's partner in cruelty, exercising tyranny alongside him, while in other versions he would beat her as it suited him.
Conomor's first wife, Cormelian. A woman as twisted as the young Conomor, who enjoyed indulging in Conomor's self-centered tyrannical ways with him. However, when the prophecy came that Conomor's child would kill him, she was already pregnant, and she refused to "deal with it" despite her husband's urging. Seeing this as a betrayal essentially resigning him to death, Conomor took the matter into his own hands, killing Cormelian with his own hands to preserve his own life. Despite this, Cormelian was probably the person who came the closest to reaching his heart, only making him even colder afterward.
Conomor's second wife pulls from his role as the base for King Mark (Tristan's Uncle), namely Isolde. Isolde was a bride he chose for political ties, and Conomor had her escorted from her homeland to his territory, but along the way Isolde fell in love with another man. Because of this, Isolde resolved that she would "do her duty" as Conomor's wife (read: produce him an heir) and then leave him at the earliest opportunity to marry her true love. Conomor, knowing she had feelings for another man, didn't tell her about the prophecy or what happened to his previous wife who tried to give him an heir, because he feared that if she knew his death would be assured then she would use it to kill him and run off with her lover. It backfired massively, and when she got knocked up he killed her too.
Conomor's third wife pulls from Bluebeard; Anne was a beautiful commoner lady who caught the eye of the terrible lord and was taken to be his wife with no room for objection. Conomor wanted to silence the attempts by other lords to try and force political marriage on him to take control of the english channel he was monopolizing, specifically his long time rival the lord of Vannes. To do this, he picked essentially the first passable woman he found that had no backing and thus no way to threaten his position politically. Anne was believed to be barren, which was an even bigger plus, because it meant Conomor wouldn't have to kill her. Unfortunately, that's not the case; her body was exceptionally compatible with Conomor's, and before long they conceived and the writing was on the wall.
The last of his wives was based on the historical Conomor's famous wife, Trephine. The daughter of the lord of Vannes, Trephine was married off to Conomor as soon as was feasible after Anne's passing. Vannes wanted stake in Conomor's land and his beautiful daughter was a small price to pay. Conomor, a paranoid monster by this point, didn't care at this point, justifying to himself that Vannes could never take it from his cold dead hands if he continued to never die. Trephine, for her part, genuinely wanted to help Conomor and to ease the long-standing tensions between him and her father, but it was far too late to save his soul by then. But not too late to save her own; although too late, Trephine's ability to commune with spirits allowed her to receive warning from Conomor's previous brides, who told her of how they died and urged Trephine to run and hide before Conomor found out that she was able to bear him an heir. With that advance warning, Trephine was barely able to escape him and have their child, but Conomor tracked her day and night like a maddened bloodhound until she was ultimately slain too.
However not before Tremeur (their son) was set to be raised by the local church, and eventually learned of his heritage and led a rebellion against the tyrant lord Conomor, ultimately being the one to slay him. The prophecy came true, though Conomor rose again in death, unbeknownst to most. Survival at the expense of all else is the one thing he's good at, after all.