Imam Mahdi (PBUH) in the words of scholars 5

Greater than Imagination...

I caot refer to him as the leader, he is greater than this. I caot say the he is the first person, because there is not any second person (throughout the ranks)! We caot describe him with any description other than “The Promised Mahdi”. He is the one that God has saved for the mankind.
imam Khomeini

Sahifeh-of Imam, volume 12, p 482