Elven Ranger Corps
The Elven Ranger Corps was a high elven organization that encompassed the elven rangers of Quel'Thalas, masters of marksmanship and scouting. It was charged with the defense of Quel'Thalas and led by the Ranger-General of Silvermoon, leader of the high elves' military forces. During the Third War, this organization was led by Sylvanas Windrunner. The Elven Ranger Corps met Arthas Menethil at the borders of Quel'Thalas and fought the traitorous prince every step of the way, through both the Inner and Outer Elfgates, back towards the high elven capital.
It is mostly likely the "Elven Ranger Corps" has been retconned to being named Farstriders instead, as they have not been mentioned in more recent sources and the term Farstriders was used to refer to the ranger organization in the past events and during the Third War.