Mark Moonrider was a member of the Forever People, a team of teenagers who journeyed to Earth-One escaping the persecution inflicted on them by Darkseid of Apokolips. Leaving behind their native Super Town which hovered over planet New Genesis, they had several adventures before being banished to another dimension.
Roy Lincoln was a chemist who after a brief superheroic career on Earth-Two wherein he became a member of the All-Star Squadron, he journeyed to the parallel planet of Earth-X which had no heroes alongside the Freedom Fighters to free that world from Nazi oppression.
Both Mark as Moonrider and Roy and Human Bomb had explosive powers. Moonrider had a megaton touch, while Human Bomb had his 27-QRX formula powered touch. As such, Roy has to wear a protective suit, while apparently the Mother Box that Mark's team uses controls his power.