King Thanos made his debut not so long ago in November 2017. You can find him in Thanos Vol. 2 #13. He was created by Donny Cates and Geoff Shaw. He lives in a parallel universe, Earth-TRN666.
In terms of power and abilities, they are the same as the ones from the other universes only he seems to be significantly stronger as he even keeps the Hulk as a dog.
In terms of the story, King Thanos is still in love with Death and tries everything to please her and in this universe, he has tried everything. He has killed almost every hero and opponent that ever crossed him and now rules the universe where there’s actually nobody left.
But here comes the catch, in order for King Thanos to be with Death, he has to die which has become nearly impossible. Therefore he has tasked his servant The Rider to go back in time to find his younger self and bring him to him. So his younger self could finish the job and kill King Thanos. The Rider uses the Time Stone that he received from King Thanos and goes back in time to find young Thanos.
As soon as young Thanos is being confronted with King Thanos, he engages in an attack and he is convinced that King Thanos is an imposter. King Thanos is able to convince his younger self of his true identity by revealing his original name that his mother wanted to give him at birth which is Dione.
Not much later, the Fallen One arrives at King Thanos’ doorstep backed up by his entire Annihilation Wave. King Thanos and young Thanos decide to fight side by side in order to defeat the Fallen One and his army which they eventually do. Quickly after that, young Thanos learns that this was King Thanos’ plan all along in order to be together again with Death.
Therefore old Thanos decides to attack his younger self to have one last fight but his younger version quickly overpowers him and King Thanos begs for death. Young Thanos is completely disgusted by his older self and steals the Time Stone and returns to his own time. Upon his return, young Thanos decides not to become like his older self.
As Thanos never becomes King Thanos that timeline is completely wiped out. Nevertheless, we still encounter King Thanos in his final moments alongside Death. He demands to know what happened to his younger self and Death reveals that his younger version won without even lifting a finger.