It can be said that it was more the cost of maintaining the frontier which stopped Roman expansion into the north/northwest more than any single tribe. It was easier to form a boundary by combining geaographical features and treatied tribes and call it good...lol
There were primarily two Germanic tribes that toppled the western Roman empire: the Visigoths and the Vandals with additional pressure coming from the Huns. These tribes were from the east (Dacia) with is the modern day Balkan region.
Alaric, who eventually conqured and sacked Rome, was both a Goth and a Roman citizen.