Arek (or Lord Alekdias), who is first introduced in Lufia II: Rise of the Sinistrals, is the king of the Sinistrals. His full title is Arek the Absolute. Unlike the other 4 Sinistrals, he is more of an observer throughout the course of events and has not been shown threatening non-gods. He is rarely shown on-screen in any of the games. He is also not shown engaging with anyone but Erim. His fate throughout the series is left unknown.
Arek is shown during the prologue, wearing a king's garb and sitting on an unknown throne. Arek is shown talking to Erim as to whether the Sinistrals or humans will rule the world. He only asks because of the Dual Blade's judgment. Arek sends Erim to investigate the blade's status.
Late in Lufia II, Daos claims that Arek has the power to twist fate. The crisis of the Sinistrals was supposed to bring out good superbeings as well as evil ones (the Sinistrals); however, Arek somehow prevented the good superbeings from appearing.
While Arek does not appear in the game, he is mentioned by Iris. If you made it past floor 200 in the optional Ancient Cave and defeat Iris, she will mention such thought of you being strong enough to defeat Lord Alekdias (Arek). SHe later shrugs the thought.
Arek does not appear until at the endings of the game, but plays a major role of events once revealed. His appearance is shown as a "blue crystal" with debris encircling around him in an unknown white-dimensional location that looks like it has remains of Doom Island.
In Caldio Shrine, Daos mentioned to the heroes that Arek warned him about the Dual Blade.
On the first ending, Arek asks Iris of her observation of humans. He respects that humans are capable of good things when Maxim and Selan sacrificed their lives to save loved ones. With doubt of gods fading out, he wonders why Iris saved Maxim. Noticing Iris' feelings towards Maxim, Arek presents her with the Dual Blade and knows that the journey isn't over for either humans nor gods. The reason why Arek showed Iris the Dual Blade was due to its ability to manipulate time and that he believes Iris has not fulfilled her true resolve. Time is going backwards, perhaps to change past events, leading to New Game+.
On the second ending, Arek shows satisfaction that Erim was the first Sinistral or God to express attachment to humans and to willingly sacrifice herself for Maxim and humans in general respectively. During the game's alternate ending, he vows that Erim's sacrifice will not be in vain. He mentions that the Dual Blade wants an endless adventure towards the future. It is hinted that the Dual Blade is even more powerful than Arek himself. His fate is left unknown.