The German government is the member of the Central Powers of World War 1 that put Lenin on a train back to Russia.
The February 1917 Russian Revolution brought Lenin back to Russia. He had been living in Switzerland at the time and the revolution took him by surprise. The German High Command arranged for Lenin to be transported from Switzerland to Russia in a diplomatically sealed train. The Germans wanted Lenin to create more revolutionary disruption in the hope that a new Russian government would get Russia out of World War I.
By a special train with other trains acting as decoys.
It was a diplomatically-sealed train originating in Switzerland and bound for Russia, traversing Germany and Sweden. The Germans allowed the transit, not taking any chances that Lenin would disembark in Germany to spread his Communist propaganda, but fully welcoming the idea of him inciting revolt in Russia, which was at war with Germany. For this, Lenin's foes in Russia had denounced him as a "German spy". While he most likely was not anybody's spy, the revolution he eventually led certainly played into Germans' hands.
Vladimir Lenin was sent back to Russia by the German government in April 1917 in the hopes that he would disrupt the Russian war effort or even cause a revolution to get Russia out of the war.
Lenin was isolated in neutral Switzerland during the beginning of World War I. After receiving news of the February 1917 Revolution in Russia, he wanted to return there immediately to give instructions to the Bolsheviks about how to continue with the revolution and to defeat the Provisional Government. A Swiss Communist convinced the German government to send Lenin safely to Russia on a sealed train. The German government hoped that Lenin would provoke political unrest in his homeland, forcing Russia to surrender to the Germans, which would allow Germany to pull troops away from the Eastern Front to focus on the war in the Western Front.