Ultra Dark-Killer

Ultra Dark-Killer (ウルトラダークキラー), or simply Dark-Killer, is the primary villain in the pachinko game, Ultraman Taro: Revenge of the Dark. He also appears in various stage shows and events and most recently, Ultraman Festival 2017. In 2019, he makes his first on-screen appearance in Ultra Galaxy Fight: New Generation Heroes.

Ultraman Taro: Revenge of the Dark
Dark-Killer was said to have been born from the grudge of various monsters and aliens destroyed by the Ultra Brothers, much like Grand King and Tyrant. However, unlike those two monsters, Dark-Killer was capable of reasoning and conversation.

He harassed Taro by reviving several monsters to weaken him before covering the Earth with the Killer Plasma effect. Although he initially overpowered Taro in their duel, he was defeated when the Ultra Brothers, from Zoffy to Ace, appeared and merged with Taro to grant him his Super Taro form. Defeated by an Ultra Dynamite, Killer's eyes turned blue as he encounter a new emotion, brought on by Taro's self-sacrifice.

Despite his defeat, Dark-Killer later returned, driven and revived by his hatred for Taro. At this time he learned to use the Killer Plasma attack to separate his body and create the Ultra Dark Killer Brothers, dark doppelgängers of the Ultra Brothers that assisted Taro in their last fight. He then attacked Ultraman Mebius and the real Ultra Brothers, but was driven off.

Later he would appear and attack Ultraman Zero, but was once again defeated.

Ultra Galaxy Fight: New Generation Heroes
Ultra Dark-Killer has revived and teams up with Dark Lugiel and Etelgar to fight against the New Generation Heroes. He steals the light of Ultraman X and Ultraman Geed to create his minions Ultraman X Darkness and Ultraman Geed Darkness.

Dark-Killer suddenly arrives through a portal chasing Ultraman Zero to Ayaka City, where Asahi Minato/Ultrawoman Grigio was training. He demanded that Zero hand her over, but he refuses, so Dark-Killer sends them both to his Dark-Killer Zone.

Trivia

 * Voice Actor: Koichi Toshima
 * According to the official website, Ultra Dark-Killer "was once defeated by Ultraman Taro", suggesting that the Revenge of the Dark game is canon.