Alkyone was the Captain of Queen Hippolyta's royal guard. She, along with three other Amazons, agreed to protect their Queen's life at all costs. When word got out that Queen Hippolyta was praying to the gods for a child, Alkyone believed it would destroy them.
She has always hated Diana, thinking she was the cause of all the Amazon's problems and has endlessly plotted to murder her. Her hatred for Diana is only matched by her praise for Hyppolyta and her illusions made her believe every horror she did was in Hyppolyta's name. The first time she has tried to murder Diana (who was barely born), Alkyone intruded in the Queen's rooms to slaughter the child but Hyppolyta woke up and punished her and her 3 friends by sending them to jail. Alkyone then asked her 3 friends to help her a few years later. She failed that time as well to murder the princess & was "humiliated" by Diana.
She was married to Achilles and ruled Paradise Island for a short time but her intentions were always that Hyppolyta regained her throne. The third time Alkyone wanted, she called Cottus, a slimy black monster from the depts of Themyscira, believing it was the princesse's father.
She then "killed" Achilles, but he didn't die since his heart is that of a God. Alkyone was shot down by Hippolyta and later crushed with her 3 friends by Wonder Woman when she threw the black monster on the ledge where she was standing but we may never be sure wether if she drowned or managed to survive.