Of course it would be meaningless to introduce Che Guevara to ML comrades. But nonetheless, for the newcomers, Ernesto "Che" Guevara was an Argentinian revolutionary who grew up in a petty bourgeois background. After travelling throughout South America and noticing the conditions in which the proletariat lived, he turned to marxism-leninism, later famously saying (to ML at least) "I have sworn before a portrait of the late lamented comrade Stalin that I will not rest until I see these capitalist octopuses annihilated."
He joined forces with Fidel Castro and participated in the Cuban revolution in a military capacity, as leader one of the four guerilla armies -- I am unsure of his exact rank.
After the revolution, he briefly server as minister of justice signing death warrants among other things, then later as minister of industry, working to industrialize Cuba under the embargo.
He left in the early 60s to fight in other revolutions, notably in Congo and afterwards in Bolivia, where he was betrayed by his own and delivered to CIA-backed troops.
While his book on guerilla warfare is often left behind -- mainly, as I've heard, because it was not universally applicable and some lessons proved wrong in time -- it was still among the first books on guerilla warfare to be written. Che was indeed one of the pioneers of guerilla warfare, whose tactics he used successfully against the Batista forces in Cuba. At the very least I know it's required reading for officers in the US army (I don't remember where I read that, maybe in an article someone linked on Lemmygrad) and while the US army is completely left behind in terms of power today, they have a long tradition from which we can take the useful bits (though I am also interest to know what, say, Chinese officers read in their academies!)