Original: They were sometimes referred to as the "long-haired kings" (Latin reges criniti) by contemporaries, for their symbolically unshorn hair (traditionally the tribal leader of the Franks wore his hair long, as distinct from the Romans and the tonsured clergy).
Simplified: They were sometimes referred to as the "long-haired kings" (Latin reges criniti) by people of the time, for their symbolically unshorn hair (traditionally the tribal leader of the Franks wore his hair long, while the warriors trimmed theirs short).