Who is this "legion" I am not a big Superman lore fan, but I do love Smallville.
The Legion began during the Silver Age, when it was in-continuity in the comics that Superman had begun his costumed career in Smallville as Superboy. The Legion that originally appeared in a Superboy story in 1958 were representatives of a larger team of super-heroes from the 30th Century who traveled back in time to initiate Superboy as a member. They continued popping up in both Superboy and Supergirl stories, becoming a popular enough feature that they were given their own series. Along the way, their membership grew with each appearance. They wound up being established as a team that was usually 18 to 25 strong, based on Earth and largely human-looking, but each of them possessing a unique power in the group, with many of them being from other worlds where everyone had the same power. All of them were teens (at least when they joined), and they operated in a sci-fi setting. Superboy continued to serve as a regular member via time travel. (Silver Age Supes could travel in time under his own power.) They usurped Superboy's own title not once but twice...first with Adventure Comics
, which became their first regular series in the '60s...then in the '70s they turned Superboy's own title into Superboy and the Legion of Super-Heroes
, and eventually just Legion of Super-Heroes
. The Legion enjoyed a sort of cult popularity akin to Star Trek amongst comics readers in part because, while they fit into the larger DC multiverse of the era, their future setting allowed them to grow a mythos all their own that didn't have to tie in directly with the contemporary setting of other DC titles.
Regarding the trailer...Cosmic Boy looks a little scruffy--he was always portrayed as the straight arrow. The Persuader--wow, dead on.