Beyond the founding Avengers there are two who have grown significant in light of recent films: Hawkeye & Black Widow. Both of them began as foes to Iron Man and have since proven themselves to be stalwart Avengers and iconic heroes. In Westeros their counterparts are also heroes, though of a different sort to the warrior and knights that make up the Westeros Avenger founding triumvirate.
Falcon Eye, Longbow Archer of the Vale
Clint of Bar Town grew up a lowly mummer. Apprentice to a master swordsman, young Clint was about to debut a knife throwing performance that would have awed his patrons had a band of raiders not descended upon them from the mountains of the moon. Pilfering the heart-wood longbow of a slain knight he proved himself a keen archer. Garbed in the colors of House Arryn his masked costume his his low birth and earned him acclaim and an honored position in the garrison of House Arryn.
The Widow of the Rose
Little is known of the mysterious Widow of the Rose. Some say she is a handmaiden to the great lady of House Tyrell, others claim she is her own daughter. Still, others would refuse to believes such a poisoner and whisperer even exists, dismissing stories of her high-born victims as mere calumnies meant to despoil the name of the Lords of The Reach.