Arminius and the Germanic tribes
Arminius was a German Chieftain of the Cherusci tribe who betrayed his Roman general Varus of whom he was an auxiliary officer. This betrayal allowed him in 9 AD to annihilate three roman legions (legio 17, 18, 19) in the Teutoburg forest.
The battle which was basically a carefully planned ambush lasted for over 3 days and was to see 20,000 dead legionnaires. Varus committed suicide rather than be captured. His example was followed by many of his higher ranking officers.
The defeat of three of his finest legions badly angered and upset the Emperor Augustus. He refused to shave (as in mourning) and could be seen banging his head off walls in his palace on Palatine hill shouting "Varus, Give me back my legions"
Arminius hold over the German tribes waned after they suffered several defeats to the Romans under the general Germanicus and he assassinated on the orders of rival Germanic chiefs.
The Romans ultimately recaptured the standards of the three legions defeated in the forest. Despite these victories, the battle effectively halted Roman expansion at the Rhine.
Its an interesting fact that the shame of the legions involved was so great and their recovered eagles now seen as unlucky that the 17th, 18th and 19th legions were never reformed and passed into history.
For centuries Arminius was largely forgotten until the reunification of Germany in the 19th century inspired nationalists to use his struggle against Rome as a rallying cry. Today Arminius is seen as a hero of an unified Germany.