Archon

The archon was a heavy protoss being formed when two templar merged into a single creature of raw psionic energy. Held aloft as a hovering entity rather than a constructed machine, the archon was neither truly biological nor mechanical, and could strike both ground and air targets with an energy attack that scattered destructive force across everything near its point of impact. It was among the protoss arsenal's most powerful weapons, and one of the costliest, since each archon demanded the sacrifice of the two warriors who formed it. (StarCraft (manual); StarCraft)

A being formed by merging#

An archon came into existence through the merging of two templar, who gave up their individual bodies to become a single entity of psionic energy. A standard archon was formed from two high templar of the Khalai, while the Nerazim could fuse two dark templar into a dark archon. The merge was costly in every sense, consuming the two warriors who chose it, which necessarily limited the number of archons any protoss force could field and ensured that lesser units remained a vital part of protoss strategy. (StarCraft (manual); StarCraft; StarCraft: Brood War)

The resulting being was unusual in its very nature. The archon was neither biological nor mechanical, a quality that set it apart from nearly every other unit on the battlefield. It hovered rather than walked, and its attack, though it appeared at a glance to be a melee strike, was in truth a short-ranged discharge of energy. That attack struck both ground and air targets and scattered destructive force across everything near the point where it landed, so that attacking groups of clustered enemy air units made an archon far more efficient. An archon invested nearly all of its durability in its plasma shields, which meant it took full force from every kind of attack and was acutely vulnerable to weapons and abilities that stripped shields away. (StarCraft)

The cost of the joining#

The merge that created an archon was not a simple pooling of power but a true fusion of two minds and bodies, and the protoss who underwent it did not always survive the experience whole. The licensed expansion StarCraft: Insurrection, whose place in canon is uncertain, illustrated the toll through the being known as Aedus/Xerxes. Aedus and Xerxes were two high templar who held a deep love for each other and who merged into a powerful archon early in the Great War against the zerg. In the joining, Xerxes was said to have died, and his love for Aedus twisted into bitterness. The combined being fell ever deeper into self-loathing, existing only to hate and hoping to fall in honorable combat. The archon's strength, in this telling, was inseparable from the sacrifice and loss that produced it. (StarCraft: Insurrection)

Dark archons and protoss history#

The creation of the dark archon, formed by merging dark templar rather than high templar, was banned during the era of the Nerazim exile, and the prohibition reflected the unease that surrounded the practice. During the conflicts on Shakuras, dark archons were nonetheless created when the situation demanded them, and the threat of Amon led the protoss to authorize them again during the End War. Across these conflicts the archon, whether of the light or of the Void, remained a weapon of last resort and of great power, made each time by the willing surrender of two protoss into one. (StarCraft: Brood War; StarCraft II: Legacy of the Void)