The Imam Al-Mahdi (AS) will have when he will re appear ten thousand sincere assistants who will lead and help people all over the world, out of them 313 will be the most pious and most sincere and most able to help the aim of the Imam (AS).
The 313 assistants will be regular individuals or scholars or leaders who have that high degree of sincerity and dedication to Allah (SWT). Many of them will be unknown to people because their sincerity stops them from seeking publicity, name or fame but known to Allah (SWT) as very humble and dedicated and pious. They will be men and women as well and from different parts of the world.
Wassalam.