R. Yohanan

R. Yohanan said: What a mighty deed [of R. Meir's] to burn his master with fire! Only one such sinner was in our midst, and we could not save him! If Elisha had been in my care, who would have dared snatch him from me? So he said: When I die, I shall extinguish the smoke from Elisha's grave. When R. Yohanan died, the smoke ceased from Aher's grave. Then the public mourner began [his oration] concerning R. Yohanan thus: Even Gehenna's gatekeeper could not stand up to you, O master!

Here is a beautiful example of a Rabbi having the power to overturn G!d's ruling. Earlier, Aher hears a Bat Kol telling him that he cannot do Teshuvah and be saved from Gehenna. But after Aher's death R' Yohanan saves him from Gehenna by his prayers.