Algol is a character in the Soul series of fighting games and one of the main antagonists of Soul Calibur IV. He can be played like other standard characters, but must be unlocked by defeating him in Story Mode. He appears as one of the final bosses along with Siegfried and Nightmare. Algol has also returned for Soul Calibur: Broken Destiny and Soul Calibur V. As the original wielder of Soul Edge, likely responsible for much of its power, and the creator of Soul Calibur, he is ultimately the cause of the events of the series as a whole.
What lies in his soul is Absolution.
In Soul Calibur V's promotional material, he is referred to as "The Great Hero King".
In Soul Calibur II's Weapon Master mode there is a country called "Algol", likely named after the star, as are the other countries.
When Soul Calibur III was in the making, the preview sites stated that Soul Edge was once used by "a king who was forced to kill his son".
Algol, also known as "The Hero King," was able to obtain Soul Edge, and with his indomitable will, he resisted the sword's control. According to the legend, he used the sword to spread peace among the lands, building the Tower of Glory as a monument to his reign. His son, Arcturus, jealous of his father's power and unaware of the sword's malevolent properties, stole Soul Edge for himself and was possessed. Faced with no other choice, Algol battled and defeated his son with a fatal strike.
Deeply remorseful after his son's death, Algol endeavored to create a sword to counter the evil within Soul Edge. The legend says that, using purified shards obtained from the battle with his son and the assistance of various sages, Algol was able to create Soul Calibur after many failed attempts and the sealing of his own soul inside the Astral Chaos, leading to the creation of Soul Calibur's spirit. However, the "successful" ritual produced unexpected results: the blade created was extremely similar in nature to Soul Edge due to the restlessness in Algol's soul. The tribe that was tasked with the protection of the new sword slowly purified it into the weapon as it appears in the series, sealing the Hero King's soul, keeping his thirst for power dormant over the centuries. Within the Astral Chaos, Algol's soul fell into a deep slumber. As he slept, the chaotic energies of Astral Chaos transformed his soul into an avatar of war and domination.
During the immense surge of power released when the cursed sword and the spirit sword clashed, Algol's soul, then formless, awakened and absorbed a small fraction of the energy. With what little he gained, he built himself a physical body fashioned after his older one as well as a tower built in the image of his old Tower of Glory, which he deemed the "Tower of Remembrance", to reside in. Algol knew that it all would not last—once the power he absorbed had been exhausted, everything he created would disappear like a mirage. He needed to obtain the swords if he intended to remain a reality. The Tower of Remembrance's sudden appearance would draw warriors to him. The swords, he knew, must be amongst them. Forging himself weapons based on memories of the cursed sword and the spirit sword, he waited patiently for the first arrivals.
When Nightmare opened a portal to Astral Chaos, Algol desired to conquer the mortal realm. He clashed with Mitsurugi, but during their fight Soul Edge was destroyed and Algol was pulled back into Astral Chaos. Always a man in search of a conquest, Algol placed his eyes on taking over the real world by corrupting it with the energy of the Astral Chaos. In trying to do so, he's attempting to control the energies of the realm, which forms his ethereal body.
Edge Master is the only one who notices this "corruption" going on, and has entered the Chaos to fight the Hero King. However, he's not sure he can keep up with him, even if going all-out.
Algol desires to reclaim Soul Edge - which he considers to be the symbol of his power as the ultimate ruler, and Soul Calibur - which he considers to be symbol of his time as a mortal king - as he believes they are the only weapons worthy of being wielded by him.
Algol awakens when Mitsurugi battles Iska Acht in Astral Chaos, Algol speaks to the duo recognizing Mitsurugi due to having fought his original timeline counterpart and thus tells the warrior to seek him out for a "rematch".
He is reprised by Jamieson Price in the English dub and Jouji Nataka in the Japanese dub.