Einherjar Eight Warriors

The Einherjar Eight Warriors (アインヘルヤル八闘士) are a group of eight Mutos Reploids in Mega Man Zero 4.

History
The Einherjar are a task force assembled by Dr. Weil to oversee Operation Ragnarok, destroying all inhabitable areas outside Neo Arcadia to discourage anyone from running from Weil's rule.

Once the Eight Warriors are defeated by Zero, Weil transmits a message to Area Zero, proudly proclaiming that all the Resistance’s efforts are futile; the Einherjar were only a distraction  so that Weil could finish construction on the Ragnarok space station.

Even though Weil was apparently killed during Craft's rebellion (the latter having fired Ragnarok's laser on Neo Arcadia, destroying it) the Resistance learns that Ragnarok's threat is far from over, since it's now descending to Earth. Zero enters the station one more time, and faces the resurrected Einherjar once more. It is heavily implied that Weil had resurrected the Eight Warriors as part of the line of defenses against Zero and the Resistance stopping the descent of Ragnarok. Zero defeats all of them a second time before going on to face Dr. Weil himself.

Members
Under Craft's command, they were tasked with missions that would disrupt life in various ways in Area Zero.
 * Sol Titanion took control of an artificial sun. The sun's rays are amplified to unbearable (even for Reploids) temperatures, turning the surroundings into a desert wasteland. Zero destroys the sun's generators and shuts it down for good when he takes down Titanion herself.
 * Heat Genblem uses his own body to power a mobile particle cannon headed towards Area Zero, periodically firing devastating beams to ravage the landscape. Zero infiltrates the weapon by going through its barrel and defeats Genblem, leaving the cannon without a power source.
 * Popla Cocapetri infects an ancient mechanical city with a computer virus, intent on using it as a frontline base and environment destruction weapon against Area Zero by having its development program go out of control. Unfortunately for him, Zero fights through the city's automated defenses and destroys the diminutive Reploid.
 * Pegasolta Eclair pilots a massive aerial fortress towards the Settlement, using acid rain to kill the plant life below. Zero invades the fortress, destroying the generators responsible for the lethal precipitation before doing the same to its Einherjar commander.
 * Mino Magnus activates a massive electromagnetic generator, creating an abnormally large and excessive magnetic field that begins to disrupt the surrounding area in attempts to destroy Area Zero's self-regulating environment technology. His plans never reach the Settlement, as Zero fights his way through the generator and destroys Magnus, stopping the waves from wreaking havoc.
 * Noble Mandrago uses plant-like nanomachines that threatens the natural wilderness by forced accelerated chemosynthesis of the soil, invoking erosion, infertility, and reducing sustainability, in an attempt to reduce Area Zero into a wasteland. In turn, Zero cuts through the false jungle to reach the Reploid controlling it, who he destroys in battle shortly afterwards.
 * Tech Kraken causes earthquakes with a drill-equipped submarine, threatening to demolish Area Zero and the Resistance Base. Navigating a complex underwater maze, Zero confronts Kraken, who reveals his ulterior motive for joining the Einherjar: defeating Zero to avenge his late master, Hidden Phantom. Nonetheless, the red Reploid defeats the Zan'ei soldier, ending his part in Weil's plot.
 * Fenri Lunaedge reactivates a facility containing old, potentially dangerous experiments. Zero overcomes the security system and rogue projects on his way to the building's final chamber, where he destroys Fenri and shuts down the facility.

Etymology
In Norse mythology, the einherjar are those that have died in battle and are brought to Valhalla by valkyries. They prepare daily for the events of Ragnarök, when they will advance for an immense battle.