Was/Is Lenin treated as a traitor for working and being paid by Germany in WWI or was it hidden or justified in some way? If and how perception of him changed in XX and XXI century from Russian people/historians/universities pov?
Depictions of Lenin's relationship with the Germans in 1917 is one fraught with a lot of mythologizing and hand-wringing. The charge that Lenin was a German agent and took the Kaiser's gold was one that dogged Lenin when he arrived back in Russia and some of the earliest anti-Bolshevik campaigns portrayed them as the catspaws of the Germans. For their part, the Bolsheviks played up the dramatic elements of their return from exile and erased any questionable decisions from the narrative. The reality, of course, was much more prosaic. Lenin was neither a German agent nor a traitor working for the German government, and both used each other tactically during this period for their own ends. Far from being dramatic spy story, the story of the Bolshevik's return was a somewhat dull affair.
The famous sealed train is an exemplifies how politicized narratives often trumped the quotidian reality. Despite cinematic depictions of the train that have Lenin and his compatriots locked in (eg the BBC miniseries The Fall of Eagles) the train itself was not really sealed. Russians had their own special cars and shared dining and bathroom facilities. The partitions were not locks and chains, but rather a border line drawn by chalk and enforced by a German officer. The Russian emigres were allowed off at stops in Germany to buy beer and newspapers, and some members of the delegation talked with German workers.
Contrary to its immediate and subsequent mytholigization by the Bolsheviks, the security details on the train were actually a way to protect its Russian passengers. Lenin's decision to accept German assistance while in Switzerland was a controversial move in the emigre quarters in Switzerland. Russia and the Provisional Government were still at war with Germany and there were divides within the Russian radical community as to which side to favor. Some in the Mensheviks wing of the RSDLP perceived that a German victory would undo the bourgeois revolution achieved in February and that Russian victory was desirable. Although there were some well-wishers when the train departed Switzerland, there were also cries of "pig" and "German stooge" as well. Moreover, the sealed train also protected the Bolshevik delegation from the charge of collusion with the Germans, which would have given the government a pretext which to lock Lenin up for treason. Both in form and intent, the security measures on the train were the exact opposite of how the Bolsheviks would subsequently portray them; rather than being treated as an ideological bacillus quarantined by the reactionary Junkers lest they infect the German proletariat, the lax security measures were actually a reflection of Bolshevik political weakness.
Herein lies one of the key mythmaking stratagems of the Bolsheviks. The Soviet state narrative of the events of 1917 was that all roads of revolution led to Lenin. Lenin's return at Finland Station was the natural evolution of revolutionary forces and everyone at the time recognized this. However, the Bolsheviks were only one of several revolutionary groups in operation at the time and the mantle of "heir of the revolution" was quite contentious. Lenin responded to this environment tactically and gambled that German help might cost in the short-term but allow the Bolsheviks to be on the ground in Petrograd before other exiled radicals. These groups were much larger than subsequent state memory would hold and the Germans supplied money to them as well. German funding efforts actually tended to favor the Socialist Revolutionaries who were a much more established political group than the RSDLP and whose policies were less aggressive. This erasure of Lenin's rivals was not just a feature of the Soviet state. Among the anticommunist right and the Whites, the idea that the Bolsheviks were German stooges became an article of faith. The irony was that White groups tended to be the main beneficiaries of German funding and war material in the Civil War. Anticommunist historians in the Cold War like Richard Pipes further entrenched this idea that the Bolsheviks seized power in a coup funded in part by Russia's enemies.
This created an odd congruence between the official state historians and anticommunist Russia specialists in the West when the so-called Revisionist historians of 1917 like Alexander Rabinowitch and Sheila Fitzpatrick began publishing in the 1960s. These historians began to look at the Revolution from the bottom-up and found that although the Bolsheviks enjoyed a degree of popular support, they were as more led by events rather than controlling them. These findings undercut claims towards Lenin's uniqueness, but also to the idea that small ideological clique seized power in a coup. Thus the Revisionists were not only attacked in the Soviet press, but also the in various publications in the West by the Cold War mandarins of Russian studies and Kremlinology. But the work of the Revisionists endured both of these assaults, and emerged as one of the dominant interpretations of 1917.
The Revisionists gained some inroads in the late-Soviet university during the Gorbachev era as the spirit of Glasnost fostered a renewed interest in the popular origins of 1917. However, revising the tale of 1917 carried relatively little political weight in the post-1991 milieu. The Second World War had displaced 1917 as the cornerstone of national legitimization and public memory long before Gorbachev and Yeltsin (and continues to do so- this podcast with Elizabeth Wood explores some of the Putin-era memory cultures and is worth a listen). Demythologizing Lenin thus was not as contentious as other issues in Soviet history like the Molotov-Ribbentrop Pact and 1917 became a very distant memory that was disconnected from wider political life.*