An Intercessor is defined as
 ""One who goes between, or intercedes; a mediator. (a) One who interposes between parties at variance, with a view to reconcile them. (b) One who pleads on behalf of another."

"Isaiah 59:15-17 
15) Yea, truth faileth; and he that departeth from evil maketh himself a prey: and the LORD saw it, and it displeased Him that there was no judgment. 

 16 )And He saw that there was no man, and wondered that there was no intercessor: therefore His arm brought salvation unto Him; and his righteousness, it sustained Him. 

 17 )For He put on righteousness as a breastplate, and an helmet of salvation upon His head; and He put on the garments of vengeance for clothing, and was clad with zeal as a cloak."

"Romans 8:26-27 
26) Likewise the Spirit also helpeth our infirmities: for we know not what we should pray for as we ought: but the Spirit itself maketh intercession for us with groanings which cannot be uttered. 

 27) And He that searcheth the hearts knoweth what is the mind of the Spirit, because He maketh intercession for the saints according to the will of God.