Arminius (a Latinized variant of a German name, which is unknown, but was for sure not "Hermann") was the son of a Cherusci war chief named Segimer. As a young man, he served as an auxiliary in the Roman army, probably fighting other barbarian tribes in the Balkan peninsula.
He returned home to Germany, where the Roman Empire had established control of the territories between the Rhine and Elbe rivers, to find his people being governed by Publius Quinctilius Varus. Arminius felt that Varus, a relative by marriage of the Emperor Augustus, was treating the Germans badly and trying to Romanize them. Although Varus treated him as a trusted subordinate, Arminius began plotting to make war on the Romans.
He hatched the plot in 9 AD, probably in the fall, near the hill called Kalkriese in the Teutoburg Forest. Varus and three Roman legions totalling about 20,000 men were wiped out, and the Romans were expelled from Germany. They never again attempted permanent conquest of any territory on the right bank of the Rhine.
After his great victory, Arminius tried for several years to exercise power over the various German tribes. He also met the Romans in other battles, as they sought revenge for Teutoburg Forest. In 16, at Idistaviso, a Roman army commanded by Germanicus did manage a victory over Arminius and even captured his wife Thusnelda. However, Germanicus gained no lasting benefit from his victory, as Arminius defeated another Roman force near the Weser river and compelled the Romans to withdraw.
A few years later, after apparently gaining even more power due to the death of another German war chief, Arminius was killed, reportedly by a member of his own family.
Largely forgotten for centuries except in the accounts of his Roman enemies, some of whom highly respected him as a liberator of his people, the story of Arminius was revived in the late 19th century as part of a wave of German nationalism.
In 1875, a massive statue of Arminius was built near Detmold, about 75 miles from the presumable Teutoburg Forest battle site. It still stands today.