Brother from Another Planet (遊星から来た兄弟 Yūsei Kara Kita Kyōdai) is the 18th episode of Ultraman.
When a toxic fog falls over Tokyo and starts affecting the people the SSSP goes to investigate. There Arashi and Ide spot the Alien Zarab I in disguise. At first they fear it is hostile but the alien claims to be the friend of humanity and offers to remove the fog as proof of his good intentions.
However at the time of Zarab's good deed, Hayata was investigating a missing space shuttle that suddenly appeared back in the Earth's stratosphere. When Zarab removed the toxic fog from Tokyo, it was sent in into space, along with the space shuttle. While Zarab had gained Earth's favor, the SSSP had Hayata keep a close eye on him.
When Zarab took his leave from Earth to return to his ship, Hayata followed him. Hayata discovered that the Zarab man's ship was actually the missing space shuttle and he had enslaved its crew. Before Hayata could return to Earth, Zarab revealed that he had been aware of Hayata's presence since they left Earth. The alien also knew that Hayata was the human host of Ultraman. After revealing his true intentions the man of Zarab imprisoned Hayata, then returned to Earth disguised as Ultraman and briefly began to destroy the city of Tokyo, planing to use Ultraman as the means to cause the humans to fight among themselves.
Zarab then appeared at a council meeting and insisted that the SSSP should attack Ultraman if he returns. This caused much argument among the council members as they still had faith in Ultraman. Later that night, Zarab disguised himself again as the Imitation Ultraman and returned to his rampage. However Hoshino found were Zarab had hidden Hayata and freed him, allowing him to become Ultraman and clear the Ultra Warrior's reputation. Ultraman managed to shed the Zarab of his disguise when the impostor tried to escape. Zarab fought hard against Ultraman but was eventually killed, thus, ending his invasion.
- Toshio Muramatsu (ムラマツ・トシオ Muramatsu Toshio): Akiji Kobayashi (小林 昭二 Kobayashi Akiji)
- Shin Hayata (ハヤタ シン Hayata Shin): Susumu Kurobe (黒部 進 Kurobe Susumu)
- Akiko Fuji (フジ アキコ Fuji Akiko): Hiroko Sakurai (櫻井 浩子 Sakurai Hiroko)
- Daisuke Arashi (アラシ・ダイスケ Arashi Daisuke): Sandayū Dokumamushi (毒蝮 三太夫 Dokumamushi Sandayū)
- Mitsuhiro Ide (イデ・ミツヒロ Ide Mitsuhiro): Masanari Nihei (二平 政成 Nihei Masanari)
- Isamu Hoshino (ホシノ・イサム Hoshino Isamu): Akihide Tsuwaza (津沢 彰秀 Tsuzawa Akihide)
- Ultraman (ウルトラマン Urutoraman): Masao Nakasone (中曽根雅夫 Nakasone Masao) (grunts)
- Narrator (ナレーター Nareta): Koji Ishizaka (石坂浩二 Ishizaka Koji) (1-19)
- Alien Zarab
- Imitation Ultraman
- Ultraman Volume 5 Features Episodes 17-20.
- Ultraman Complete Series Features All Episodes.
- This episode was later featured in New Ultraman Retsuden episode 134 "A Fake Ultraman Appears!? The Brother from Another Planet".