Which emperor from Rome conquered Germany in ancient Roman times?

The Romans never set up a permanent province past the Rhine. Under the emperor Augustus, much of Germany was invaded, under the command of his adopted son Drusus, but the region was later evacuated after the "Battle of Teutoburg Forest", in which three entire legions were slaughtered (roughly 15,000-30,000 men) by the German chieftain Arminius. Augustus then sent his grandson Germanicus (son of Drusus) to engage in punitive raids against Germany in retaliation. However, not long afterwards, Augustus died and Tiberius became the new emperor. He abandoned the German frontier up to the Rhine River and the Romans didn't really return to what they called "Germania Magna" or "Free Germany" again. The Rhine and Danube more or less served as the permanent natural borders between Rome and Germany. The historian Tacitus states, "He (Arminius) was unmistakably the liberator of Germany. Challenger of Rome - not in its infancy, like kings and commanders before him, but at the height of its power - he had fought undecided battles and never lost a war. He had ruled for twelve of his thirty-seven years. To this day the tribes sing of him. Yet Greek historians ignore him, reserving their praise for Greece. We Romans, too, underestimate him, since in our devotion to antiquity we neglect modern history". The emperor Marcus Aurelius, and a few others, launched punitive raids against invading Germanic tribes but the provinces were never significantly expanded. Two provinces existed west of the Rhine called "Germania Inferior" and "Germania Superior", however, they didn't encompass much of what we now know of as Germany today. Germany was not a united state until the 1800's and was more or less a collection of tribes until they were united as the Holy Roman Empire under the rule of Charlegmagne. Germania Inferior encompassed the southern and western Netherlands, Flanders and Nordhein-Westfalen, and included cities such as Cologne, Bonn and Utrecht. Germania Superior encompassed most of Switzerland, Alsace and southwestern regions of Germany including the cities of Besancon, Mainz and Strasbourg. A "German Horse Guard" was employed by Julius Caesar during his invasion of Gaul and was consequentially split between Octavian and Antony upon his death. Octavian maintained the Guard as his own personal bodyguard during his reign as Augustus and they were used off and on by the following emperors. They are not to be confused with the Praetorian Guard, who were made up of citizens from the Italian provinces. Throughout the existence of the empire, the Germanic tribes were thought of as aggressive, warlike and backwards. They were the quintessential barbarians, so to speak and had a fearsome reputation. Historians debate whether the Romans could've maintained Germania Magna as a province but for whatever reason, Tiberius gave up on the idea and not many of the following emperors second guessed his judgement.