GM Henson Jr. is the only son of the GM Henson family, residents of Lacroa, and first appears in the first installment of the "SD Gundam Gaiden" series, "Sieg Zeon Arc." He was a baby when he first appeared. From a young age, he endured a tragic early life, constantly bullied by the Zeon Clan and Mad Golems alongside his parents.

His greatest hero was Knight Gundam, who defeated the Zeon Clan. Admiring Knight Gundam, Jr. aspired to one day become a hero of justice, helping the weak, just like Knight Gundam.

He was also involved in the birth of Santa Gundam during his childhood.

As a child, he mistook Demon Satan Gundam for Santa Claus. Later, Satan Gundam fused with Knight Gundam, regaining its original form as Superior Dragon, and thus defeating the Dark Emperor Sieg Zeon. Superior Dragon, after saving Zakrello Cat, who had become Sieg Zeon's vessel, temporarily split into good and evil, with the evil side disguised as Santa Gundam heading towards GM Henson Jr. Santa Gundam handed the Zakrello Cat to GM Henson Jr. and left, and it seems that the days he spent with this Zakrello Cat were the catalyst for him becoming a beast master later on.