I understand that these two people are viewed differently in Latin America to how they are viewed in the rest of the world. When describing them as heroes and villains I am referring to the way in they are commonly portrayed in Europe/USA/Canada etc.
Folks, I have now removed five different comments containing nothing but the quote "You either die a hero or live long enough to become the villain." This is not an acceptable answer on AskHistorians; please stop posting it.
There were some comments that were removed claiming that there was an ideological split between Che Guevara and Fidel Castro. This is untrue, as evidenced in Che's farewell letter to Fidel. Here is an excerpt:
"Reviewing my past life, I believe I have worked with sufficient integrity and dedication to consolidate the revolutionary triumph. My only serious failing was not having had more confidence in you from the first moments in the Sierra Maestra, and not having understood quickly enough your qualities as a leader and a revolutionary.
I have lived magnificent days, and at your side I felt the pride of belonging to our people in the brilliant yet sad days of the Caribbean [Missile] crisis. Seldom has a statesman been more brilliant as you were in those days. I am also proud of having followed you without hesitation, of having identified with your way of thinking and of seeing and appraising dangers and principles."
As for why Fidel is seen as a villain and Che seen as a hero really depends on who you ask. Usually, if one views Che in good light, one also tends to view Fidel in good light.
I question whether this is a proper place for this posting. It seems to me to be a current political question; why are Che and Castro viewed separately in today's political climate?
I think this is an incredibly difficult question to answer due to its highly subjective nature. For example, where I'm from(Ireland), both Ché and Castro are viewed with either indifference or extreme admiration.
I think it depends highly on the history of each country. For example, he is viewed negatively in the US as he often spoke out against the US and worked against them for most of his political life. He was seen more as the puppet master and man in charge, whereas Ché only really took off as a symbol of the Revolution after his death.
In the same vein, Ireland had the Trouble in the North in which a very Socialist leaning IRA were engaged in active armed conflict and were actively supported by Republicans North and South, and at time even covertly by our government, and many of those fighters are now in politics and government.
In contrast, Socialists and Communists in the US were not, for most of its existence, viewed with an overall positive light and were flat out crushed at various staged, especially during the era of McCarthy.
There's still the matter of Castro being alive. Death changes the view people have of someone. For example, using the Irish 1916 Rising, most people in Ireland had a highly negative view of the leaders until they were executed and thereafter were seen as martyrs. The same idea could be behind the rose tinted glasses people have for Ché but not for Fidel.
Really, I think this is a question of perspective more than it is one of fact.
koglerjs has a good point, Che would have been a much less romantic figure had he not died fighting in the jungles of Bolivia as opposed to settling down into a government position the way Castro did. A lot of Che's appeal as a heroic figures comes from his unwillingness to settle into a position within the Cuban government and its bureaucracy and instead go abroad to forment revolution in places like the Congo or Bolivia.
Castro in contrast settled down as the dictator of a country who grew comfortable, old, and fat. We got see him preside over a revolution whose lustre has worn off considerably over the years, while Che died young and fighting for his ideals, leaving us space to wistfully fantasize about what might have been and cast him in the role of heroic myth.
Which is funny, because if I had to chose between the two, I'd chose Castro. Che had a real problem with Castro and Krushchev being more disposed to diplomacy with the US and not being radical enough in formenting class warfare or exporting revolution. In fact his favoured models in this case where Josef Stalin and Mao, and he was known for being as ruthless and uncompromising (particularly when dealing with POWs in the Cuban revolution) as he was brave and committed to his ideals. (Which isn't a contradiction when you think about it. The man was a zealot.)