Garde

As they're described in I Am Number Four, the Garde are the protectors of Lorien and the ones who, in their teenage years, develop Legacies – superhuman powers to aid them in defence.

When Lorien is conquered by the Mogadorians, nine Garde children are sent away from their planet to Earth, as well as a tenth being sent separately, and before the original nine are separated, a charm is cast upon them that protects them from harm by the Mogadorians, and ensures that they must be killed in order, one through nine, as long as they are kept apart.

It is revealed in The Power of Six that they were chosen by Lorien itself to follow in the footsteps of the ten original elders. In The Fallen Legacies, Adamus counts how many of the Garde were boys and girls, but Number One as a ghost finds him and he never reveals how many. Based on evidence throughout the first three books and their prequels, it is assumed that five of the ten Garde are female and five are male.

If nature is left alone to run its course uninterrupted, the ten Garde will eventually grow into legacies that will far exceed that of the original ten elders.