"An honor to become one, they are an organization of Feywilds Knights in service to an Archfey. These knights are dispatched by the Seelie Courts to handle threats to the realms. As part of the ritual to become a Green Knight, a creature that is not an Eladrin Elf is granted their form along with powers associated." - Green Knights of the Feywild.
Around the time of the Elvish Conquests he became a Green Knight under the understanding of it as an honor. Although this being an honor is popular interpretation, the truth in Zorthas' experience is to the contrary. He would soon find out that he signed up for many activities not included in the job description and is essentially a lackey or slave to the Seelie Court's Archfey. In his experience this occupation resultantly doubles as a curse he was tricked into - a betrayal of this honor.
"The curse of Green Knights is that they cannot die without an heir to assume their place. This goes as far as denying them death of age, and any sentient or thinking creature which slays the Green Knight automatically has the Green Knight's power, status, and contract passed on to the victorious survivor. In this way there is no end to a green knight lineage. Not even suicide is an escape from the responsibilities of a Green Knight."
Zorthas despises his life, and maintains a jaded, bitterly cold attitude with a stick up his ass and a wish to keep mortals away from Fey activities precisely because of his curse. He would love to pass on his curse, but not to anybody he cares about nor can he tolerate the thought of any evil creature holding this power for any length of time.