Fortress Lad is an alien from the planet Fwang. Because that planet is constantly besieged by meteor storms, all Fwangian boys, at puberty, gain the ability to transform themselves into metallic fortresses for the protection of others.
He once saved the founding members of the Legion of Superheroes by transforming himself into what
would become their headquarters.
Years later this clubhouse became the Legion of Substitute Heroes headquarters.
The BG it's from Stephan Martiniere, here is his website http://www.martiniere.com/