Alexander Senki (Japanese: アレクサンダー戦記, Hepburn: Arekusandā Senki; lit. 'Alexander War Chronicle'), released in North America as Reign: The Conqueror, in Europe as Alexander the Great, and in South America simply as Alexander, is an anime television series that aired from September to December 1999. The series is a reimagining of the life of Alexander the Great based on the novel series Emperor's Fantasy – Alexander's War Chronicles by Hiroshi Aramata. It was produced by an international staff that drew various resources from the worldwide animation community. Character designs for the anime were conceived by Peter Chung (better known for creating Æon Flux), while it was directed by Yoshinori Kanemori [ja] and written by Sadayuki Murai [ja]. Despite being produced by Madhouse in Japan, most of the production work was actually outsourced to various South Korean animation studios.^{[citation needed]} For the original Japanese release, the opening theme song is "Let's Count Your Kisses ~You Were Mine~" (あなたのキスを数えましょう 〜You were mine〜, Anata no Kisu wo Kazoe Mashō ~Yū wā main~) performed by Yuki Koyanagi, with composition and arrangement by Hideya Nakazaki [ja] and lyrics written by Koi Takayanagi [ja]. For the American release, the opening theme song is "Worthy of Your Soul" performed by Rachael Pollack.

In the original attempt at American distribution, an English dub for the first four episodes was produced under the direction of veteran voice director Jack Fletcher. However, when the anime was later acquired by Tokyopop in preparation for a broadcast on Adult Swim under the title Reign: The Conqueror in February 2003, a new dub was created. Tokyopop retained the rights to the first four episodes of the series containing Fletcher's dub, and used them for its American release instead of redubbing them. The company then used its own dub for the remaining episodes that were not dubbed under Fletcher. Only John DeMita would return to reprise his role in the series under the alias Will Barrett, and would also take over the role of Alexander from Andrew Philpot. At some point several years after licensing it around 2002, Tokyopop let its rights to the series expire and it has remained without a licensor in North America since.

There is also a compilation film edition of Reign: The Conqueror, known as Alexander: The Movie in North America, which consists almost entirely of recut footage from the series, with the only new content being short opening and closing scenes. The movie covers the first ten episodes of the anime, ending with Alexander's victory over Darius and the Persian army.

Alexander is born a son of Philip II, king of Macedonia and Olympias, a snake witch and priestess. Desiring to attain 'speed', Alexander heads to the woods with allies Philotas and Hephaestion, where he tames a wild man-eating horse, which he names Bucephalus. At the same time he meets and befriends Cleitus and Ptolemy I Soter, recruiting them to join his cavalry. Macedonia heads to war with Athens, led by King Philip and his top advisers, Attalus, Parmenion (father of Philotas) and Antipater. Philip becomes concerned with Alexander's absence, but Alexander and his cavalry arrive at the last moment, exploiting a break in the Athenian lines and leading Macedonia to a victory. After their defeat, Athens ambassadors head to Persia, where they hope to make an alliance with new king Darius III of Persia. Alexander and his friends sneak in as Athens slaves and then kill the guards, causing Darius and his followers to think that Athens is betraying them. Darius quickly executes the Athenian ambassadors, while Alexander wanders into the Hanging Gardens of Babylon and meets a woman named Roxanne. Ptolemy is caught by the Persian army and is suspended in the air, but Alexander saves him from an execution at the last minute by releasing all the horses in the city from their stables, and creating a chaos big enough to escape with his group.

Attalus tricks Philip into thinking that Olympias and Alexander are trying to betray him. Philip banishes Olympias and marries Attalus's daughter Eurydice, who gives birth to a son that Philip plans to make his heir and future king instead of Alexander. Philip holds a great ceremony to present the new prince to the masses and also constructs a huge golden statue of himself, declaring himself a God. During the ceremony the statue crumbles, and a guard hypnotized by Olympias assassinates Philip. It is also implied that shortly after, while successfully driving Eurydice into madness, Olympias herself kills both Eurydice and her baby.

Following Philip's death Alexander ascends to King and Attalus is executed. Athens, led by Demosthenes, plots to fight back against Macedonia, doubting Alexander's strength, but relents once Macedonia defeats the powerful city of Thebes in battle. Alexander places severe demands on Athens but relents on most of them after meeting with the philosopher Diogenes of Sinope and becoming impressed by his wisdom, as well as his simple life and philosophy. Alexander next plots an attack on Persia and starts leading his troops there. Around this time Parmenion reveals to Philotas a secret about Alexander: that prior to his birth Olympias proclaimed that he would destroy the world. In addition, Aristotle, a renowned philosopher and former teacher of Alexander, sends his niece, Cassandra, to join Alexander's cavalry. Macedonia's forces continue to head through Persia's territories with multiple victories. Along the way Alexander recruits the doctor Phillipas to join him after cutting the famous Gordian's Knot (which was said that could only be undone by the King of the World) with his sword. In their next battle with Persia, Macedonia's troops are hopelessly outnumbered by Persia's, which are 10 times that of Macedonia's, but Darius tells his forces to retreat when members of the mysterious Pythagorean Cult intervene. During the battle Philotas falls off his horse and has a vision of Olympias summoning demons.

While in Egypt, Alexander meets Dinocrates, a member of his army who tells him of the great city he wishes to create there: Alexandria. Alexander has a vision of himself being in Alexandria 100 years after his death, where he visits the place where he was entombed by Ptolemy. Before leaving Egypt Alexander and his men visit the Temple of Ammon, where they witness an oracle's prophecy about Alexander being killed by the one person he trusts the most. Ptolemy witnesses a separate prophecy that tells him he will become a "Great King of the World". Plotting with Persia, Pythagorean cult members make another attempt on Alexander's life but he is able to fight them off. Darius leads Persia's armies against Macedonia's. Aristotle meanwhile meets with Diogenes, requesting the Plato-Hedron, a device created by Aristotle's teacher Plato, which contains the knowledge of the entire world. Diogenes claims however that he tossed it aside. The two watch as the battle continues. The Macedonian army gains new strength when there is an eclipse of the moon, and the Plato-Hedron appears and ascends to the heavens. As the battle nears its conclusion, Alexander kills Darius, defeating the Persians once and for all.

With Persia now part of his empire, Alexander recruits Satibarzanes, Darius's former adviser and Satrap, to become a top adviser of his. The Macedonian army becomes concerned that Alexander wants to continue heading east rather than return to Macedonia. Philotas dismisses their complaints but doesn't tell Alexander. Aristotle is also concerned with Alexander's actions and tells Cassandra that she will have to kill him should he continue to push eastward. Phillipas, secretly a member of the Pythagorean cult, plots with them to kill Alexander during his wedding to Roxanne through the use of a dancer possessing poison. During the battle she poisons Alexander but is killed before finishing him off. Satibarzanes frames Parmenion and Philotas for treason. Parmenion is killed by the plotters and Philotas is tied up and stoned to death. When Alexander arrives during the stoning, Philotas requests he let him die so as to not show weakness to the Persians. Phillipas, who treats Alexander, has the opportunity to poison Alexander but instead reveals the truth to him and provides Alexander the means to heal himself, then kills himself with the poison intended for Alexander.