Legion (Roro in the Japanese version) is a boss character in Fire Emblem: Shin Monshō no Nazo ~Hikari to Kage no Eiyū~. He is a masked Berserker working for Eremiya. He has the strange ability to clone himself, he refers to these copies as his brothers. It turned out Legion was an orphan raised by Eremiya and after his death, Eremiya deposed of his surviving "brothers" despite Katarina's protests, as she felt they were useless without Legion.
One explanation for the numerous clones is that they're each individual orphan boys raised by Eremiya but trained to work together like a hivemind, and that "Legion" is simply the leader of them.
Legion has a distinctive speech pattern, and sometimes refers to himself as "we" instead of "I".
Legion's English name is a Biblical reference to the exorcism of the Gerasene demoniac ,one of Jesus's miracles where He exorcised a man possessed by many demons:
And He (Jesus) asked him, "What is thy name?" And he answered, saying, "My name is Legion: for we are many." (Mark 5:9)
It is never clarified how much sentience his clones have, as they sometimes have dialogue, and Katarina considered it immoral for Eremiya to kill Legion's copies.
The clones are infinite, gameplay-wise. Even if you spend infinite amount of turns killing the clones, there will still be leftovers after killing the main Legion.