The Helmacrons are a fungible and egotistical species about one-sixteenth of an inch tall. Their two ships, the Planet Crusher and the Galaxy Blaster, got involved in the underground war on earth between the Animorph team (Cassie, Rachel, Jake, Marco, Tobias, and Ax) and the Yeerks because of their technology that can sense the transformational power of the blue cube and all those who can use it to morph. Yeerks had knowledge of the species' existence even though Andalites did not.
The Helmcrons are a very small species, but there technology makes up for this. They are very arrogant, perhaps even more so then the Andalites. They think that they are the masters of the galaxy, and refuse to believe otherwise.
Helmacrons are "fungible," meaning that the living absorbs the minds of the dead members of the species. Their society is based on a hierarchy with the females at the top as leaders and males at the bottom as slaves. Any major leader is killed so that she does not make any bad decisions and thus her followers can look up to her. Any disagreement between two or more Helmacrons is satisfied through bloodshed. Helmacrons can communicate through either thought-speak, or the spoken cheer "neep."
All male and female Helmacrons have a humanoid torso and four legs. Their heads resemble squashed inverted pyramids with a barbed chin, two marble-like eyes on top, and a sideways insect-like mouthpart. Females have flat heads and fierce mouthparts while males have forward-slanting heads and less horrifying mouthparts. Those who travel to distant planets wear silver one-piece suits with colored collars that identify them with a certain ship. For example, Planet Crusher uniforms have turquoise collars while Galaxy Blaster uniforms have magenta collars.
The two ships, the Planet Crusher and Galaxy Blaster, traveled to earth in search of universal domination. The Galaxy Blaster located the power source of transformation power, or blue box, in Cassie's family water pump to replenish its malfunctioning engines. Cassie mistook the ship as a toy and donated it to the charity Goodwill. It was only after she found another ship, the Planet Crusher, on the pump did she and the rest of the Animorphs suspect that they were facing a second alien invasion. The Helmacrons fought the Animorph until the aliens use the blue box to shrink Cassie, Marco, and Tobias to their own size so that the Galaxy Blaster could take Cassie and Marco captive. The rest of the Animorphs trapped the Planet Crusher in Cassie's barn and took their dead "leader" as hostages to make them tell where the Galaxy Blaster had taken the two missing Animorphs.
Cassie and Marco tricked the Helmacrons into believing that Visser Three had the blue box. They met the Visser traveling to a meeting and waged war until the Visser defeated the ship with a Dracon beam. The two Animorphs on board escaped using fly morphs and the rest of the Animorphs rejoined the two at the Yeerk meeting. The Planet Crusher escaped and took the box from Ax to shrink the Visser and Rachel. Ax regained possession of the blue box and struck a deal with the Yeerks. Cassie and Marco un-shrunk everyone and bargained with the aliens to allow them to power their engines if they would leave earth. The two Animorphs also tried to raise a rebellion among the male Helmacrons.
Both of the Helmacron ships played a key role in the Animorphs' war against the Yeerks. First the Yeerks rebuilt the Planet Crusher's morphing energy sensors to track down the Animorphs in a helicopter until Cassie took it down with her humpback whale morph. The Galaxy Blaster later returned to earth despite their previous deal with the Animorphs. The males had rebelled and split from their female leaders. Both the males and females looked for the blue box like last time and used Marco as a hostage to get the box. They both climbed into his nose to stop his heart until the rest of the Animorphs shrunk their selves down and went after the aliens, eventually getting them out of Marco's body. Once again, the Animorph team forced the Helmacrons to leave earth.
- The Suspicion
- The Hidden (Mentioned only)
- The Journey