At first, he was depicted as a caring husband and successful whaler, but Homer's behavior made Marge change the character.
Mordecai finds out their relationship and corners Cyrus Manley on top of a cliff. When he learns that Cyrus is the father of Temperance's child, he throws his harpoon at him.
Cyrus falls down on a whale, but as he announces he will be "selfish, drunk, emotionally distant, sexually ungenerous and pissy" towards his wife, the harpoon's rope becomes wrapped around Mordecai's leg, dragging him under the sea to die with his enemy.
After Homer realizes that the character was based on him, Homer decides that he'll be a better husband, proving that he is in fact different from the character despite being based off of him.