Lancer's true identity is Pisear, king of Persia. Mentioned in The Fate of the Children of Tuireann as the original owner of Lugh's terrible spear, Pisear refused the spear to Brian until he knocked his head off with an apple. He is never mentioned again.
But historically, there has never been a king of Persia by the name of Pisear. Through research of the times and of the name "Pisear" itself, it is most likely a bastardization of the Persian word Pasargadae, which was the capital of Persia under Cyrus the Great. But it also carries several other meanings. Pasargadae is also the name of the "most noble" tribe of Persia, according to Herodotus: "Now the Persian nation is made up of many tribes. Those which Cyrus assembled and persuaded to revolt from the Medes were the principal ones on which all the others are dependent. These are the Pasargadae, the Maraphians, and the Maspians, of whom the Pasargadae are the noblest. The Achaemenidae, from which spring all the Perseid kings, is one of their clans. The rest of the Persian tribes are the following: the Panthialaeans, the Derusiaeans, the Germanians, who are engaged in husbandry; the Daans, the Mardians, the Dropicans, and the Sagartians, who are nomads."
But the name of a capital and the name of a tribe can't also be the name of an individual person (in theory). Who is Pisear, then, if not Cyrus himself?
Lancer's true identity is most likely that of Darius I, the spear-carrier for Cambyses II and subsequent king of Persia after his suicide. A deliberate obfuscation of the summoning ritual and Darius' legend in order to guarantee he's equipped with Areadhbar, a form of knockoff Presence Concealment is also gained at the possible expense of skills the true Darius might have possessed.
Darius ascended the throne by overthrowing Gaumata, the alleged magus usurper of Bardiya with the assistance of six other Persian noble families; Darius was crowned the following morning. The new king met with rebellions throughout his kingdom and quelled them each time. A major event in Darius's life was his expedition to punish Athens and Eretria for their aid in the Ionian Revolt, and subjugate Greece. Although ultimately ending in failure at the Battle of Marathon, Darius succeeded in the re-subjugation of Thrace, expansion of the empire through the conquest of Macedon, the Cyclades, and the island of Naxos, and the sacking of the city of Eretria.
Darius organized the empire by dividing it into provinces and placing satraps to govern it. He organized a new uniform monetary system, along with making Aramaic the official language of the empire. He also put the empire in better standing by building roads and introducing standard weights and measures. Through these changes the empire was centralized and unified. Darius also worked on construction projects throughout the empire, focusing on Susa, Pasargadae, Persepolis, Babylon and Egypt. He had the cliff-face Behistun Inscription carved to record his conquests, an important testimony of the Old Persian language.
Darius is mentioned in the Biblical books of Haggai, Zechariah, and Ezra–Nehemiah.
The Achaemenid Empire during Darius' reign controlled the largest fraction of the world's population of any empire in history. Based on historical demographic estimates, Darius I ruled over approximately 50 million people, or at least 44% of the world's population.