There have always been heroes.  Most of the legendary personages of lore were heroes with one or more powers.  It hadn't become public knowledge until the Revolutionary War, wherein the first Legacy acted.

There has always been a Legacy since then.  The former usually dies and the first born takes up the mantle.  Each new Legacy has a new power and all the abilities of the former Legacy members.

There was a war against a Cosmic Entity named OblivAeon, who was trying to destroy the Multiverse, during which several heroes died, and some villains stepped up as heroes for the fight (some of which died in the fight).  In the end, the heroes won the fight, and OblivAeon was destroyed.

The former Legacy nearly died several times but survived each time.  He knew that the time for him to be Legacy was over though, and it was time for his daughter to pick up the mantle.  He in turn took up the name Heritage.

The Freedom Five have become both super heroes and trainers to the super heroes that have stepped up since the fight.  While most are teens still struggling with the aspects they've developed, some are adults who show up for some of the training.