Mortdecai is the name the embodiments of the three seasons, Autumn, Spring, and Summer, gave to the embodiment of winter. Mortdecai was given this name due to the fact that his season causes death, and due to the fact that the three seasons agreed that it sounded ominous, and suited winter's harsh, sinister characteristics.
Mortdecai is shunned by the other three seasons, due to his season's tendency to cause death and manifest issues. Thus, he is a recluse, the most physically inferior of the seasons, yet the most magically powerful.
He is the entity of winter, skeletal and thin, signifying winter's harsh famines, whilst his head is a skull, conveying the lives winter had claimed. He regrets the deaths caused, yet it is his duty to maintain the balance upon the earth, and so he still creates winter, each year.

(AyeSeaDee )