Zero's role as the leader of the Dark Matter, as well its capability to produce smaller Dark Matter look-alikes from its body, suggests that it is possibly a source of Dark Matter.
Overall, no background is known about it, and as such, the only hints towards its motivations are from the actions of Dark Matter. They are known to invade and infest planets such as Planet Popstar. However, it is not known what Zero intends to do with Dark Matter-infested planets. The somewhat unusual name of the Love-Love Stick, which is the weapon Kirby uses against it at the end of Kirby's Dream Land 3, suggests that it is weak to positive emotions.
Zero's body consists of a giant white sphere. In the front-center of the sphere is a single, blood-red eye with a large, dark red iris and a miniscule, black pupil.
Zero and Dark Matter are the extra, final bosses in the game. They can only be fought if Kirby has collected all of the Heart Stars; if Iceberg's Heart Stars are not collected, the game simply ends after Kirby defeats the possessed King Dedede and an ominous, dreary ending plays in which Zero appears as a shadowy figure. Together, the two evil entities are fought inside the Hyper Zone.
Right after Kirby delivers the final strike to Dark Matter, the screen begins to flash and Zero suddenly appears. The way it attacks is very similar to Dark Matter; it flies around shooting projectiles at Kirby and attempts to crash into him. It attacks by shooting blood from cuts that open around its eye and launches miniature Dark Matters at Kirby. Sometimes it moves across the screen in an erratic manner trying to ram into Kirby. Due to its size, this can be difficult to avoid. Sometimes, Zero flies forward, off-screen, and into the background. When it does, it will begin to deploy more blood from its eye, which deals damage if it makes contact with Kirby. When Zero's life meter is depleted, its eye detaches from its body in a rather gory manner and begins the final phase of the fight, with Zero's ruined body drifting away until it is off-screen. The eye will then start to circle around Kirby continuously closing in and ramming into him. Ramming Kirby is the eye's only form of attack. It does not have much health, and can be taken down in eight hits.
Once the eye's life meter is depleted, it spirals out of control, severely hemorrhaging, then explodes.
- It is stated in the Japanese-exclusive 20th Anniversary Kirby Pupupu Encyclopedia that Zero is the leader of Dark Matter.
- Despite its close resemblance to 0², and the latter also seemingly leading Dark Matter invasions, no relationship between the two has been officially confirmed.
- The Bad Boss Brothers Celebration Picture depicts all of the Kirby series' final bosses (up to Kirby Star Allies), excluding different forms of existing members or characters that are only final bosses of certain sub-games. Here, Zero and 0² are both depicted, suggesting that they are in fact different characters entirely, despite their similarities.
- Zero is the first final boss in the Kirby series to attack from the background.
- Zero, 0², Dark Meta Knight, Shadow Dedede, and Star Dream Soul OS are the few characters in the series to bleed or shed blood-tinted tears when fought.
- Zero's bloody battle did not affect the K-A rating of Kirby's Dream Land 3, but later turned the rating of Kirby's Dream Collection Special Edition from an E (K-A's replacement) to an E10+.
- This is presumably, in part, due to the fact that the E10+ rating didn't exist or have an equivalent at the time.
- Dark Matter's size in Kirby Mass Attack is similar to Zero's size.
- Zero's introduction in the Virtual Console version (and the one included in Kirby's Dream Collection: Special Edition) includes a different effect during his appearance, with less rapid flashes and a gray tone rather than bright white.
- Concept artwork seems to suggest that Zero was considered as a playable character in Kirby: Canvas Curse.
- Zero (when written in numeric form), Oro, HR-H, and Geg are the only characters in the Kirby series whose names are palindromes.
- Zero's animation of its eye bursting out of its body resembles the unused sprite of Waddle Doo in Kirby's Block Ball.
- When playing as Rick & Kine & Coo, Marx, or Gooey in the Guest Star ???? Star Allies Go! sub-game of Kirby Star Allies in version 2.0.0, Hyper Zone can be seen through a pool in the center of the arena used for the final boss rush.
- In the fourth update of Kirby Star Allies, the final opponent of the Soul Melter EX difficulty for The Ultimate Choice, Void, has a color scheme that closely resembles Zero. His splash screen also invokes the appearance of the Boss Butch's version of the Hyper Zone. With dark being one of the forms of matter Void Termina can reincarnate into, this could also suggest a deeper connection between Void and Zero.