Arstron

The monster Earthron mysteriously appeared in a mountainous region without warning or origin. It quickly made it's way toward a nearby village, setting fire to the homes with it's heat ray. MAT was on the scene soon enough, attacking the beast with their cannon fire. Mostly unaffected, Earthtron continued to destroy the village. Homes and people alike could not escape it's destruction. Goh Hideki, guided by a mysterious sense, came across an old man stuck under some debris, and a woman trying to free him. Goh lended a hand and managed to free them, before unknowingly transforming into the new Ultraman, Ultraman jack, by sheer willpower! Jack quickly turned to face Earthtron, and had little trouble outmuscling it. Jack's color timer began to blink, so he had to wrap this up quickly. Beating Earthtron into submission, and tossing him into a small crater (most likely where he came from), Jack used the Specium Ray. A direct hit on it's forehead caused it to tumble over, and explode in a display of large, blue flames.

Ultraman Mebius
This Monster reappeared in the series Ultraman Mebius.

In this series, Earthtron's origin is again not stated and his attack comes out of the blue like before, attacking GUYS HQ at a test site. However this time his actions are being guided by a Kelbeam, who is using frequency waves (originally intent to control Manquette Monsters) and directing them at Earthtron to control him (In a rather comical way.) Ultraman Mebius arrives to do battle against the two monsters who double-team him, but Team GUYS learns of Kelbeam's control over Earthtron and destroys the waves that are doing so, severing Kelbeam's control. Now free, Earthtron attacks Kelbeam, but is quickly destroyed by Ultraman Mebius, who uses his Medium Blade to cut Eatrthtron in half.