By Mark Doyle
BBC World Affairs Correspondent
Guevara's mission failed and he was chased out of the region by white mercenaries led by Colonel "Mad Mike" Hoare.
He returned to Cuba, followed shortly afterwards by Mr Ilanga, who trained as a doctor specialising in paediatric neurosurgery.
My encounter with the extraordinary life story of Freddy Ernesto Ilunga Ilanga began with a story for the BBC News website, which prompted e-mails to me from South African anthropologist Katrin Hansing.
After seeing my story about Guevara in Africa, she revealed to me her plan to make a film about Mr Ilanga's life.
Ms Hansing added another internet tale - that shortly before his death last month, Mr Ilanga had been contacted by a sister-in-law back in the Democratic Republic of Congo, who had found him via a search engine and that together they had planned a reunion after 40 years' estrangement.
That family meeting never took place, but Freddy Ilanga's amazing journey from being a teenage rebel in eastern Congo to becoming a brain surgeon in Cuba can now be told.
I first learnt about Freddy Ilanga while staying with a friend on the shores of Lake Tanganyika in eastern DR Congo.
I was compiling a series of radio and web reports for the BBC on the Congolese war, and my friend absent-mindedly referred to Che Guevara's time in the region.
"Che? In Africa?" I sat up abruptly; "Really?"
"Oh yes", my friend said, pointing up from our lakeside lodging to mountains that loomed over the water; "He was up there, in the Fizi Baraka mountains."
He tossed me a paperback version of Guevara's diary, The African Dream (Harvill Panther, 2000).
I immediately got lost in the text, and started plotting in my mind how to place the idea of some features to my editors at the BBC.
Various Congolese who fought with Guevara were still alive. On that day, two years ago, Freddy Ilanga was one.
Mr Ilanga, I learnt from Ms Hansing, was a teenage fighter for the nationalist rebel movement in Congo when, in 1965, he had a fateful meeting with Che Guevara.
For seven months, he acted as Guevara's translator in the Fizi Baraka range during the Cuban revolutionary's then-secret attempt to support the African rebels in overthrowing the corrupt post-colonial regime.
Mr Ilanga was born in 1948 in a very poor village in the far east of Congo near the border with Burundi.
He got some schooling and learnt Swahili, the lingua franca of East Africa, and French, the main language of the European colonisers.
His first job was as a newspaper vendor.
In 1964, aged just 16 and partly out of adolescent curiosity, he joined rebels fighting the Kinshasa regime.
The following year the Cuban leadership, flush from the success of their own revolution, secretly sent Che Guevara to help the rebels.
When Guevara arrived in April, Freddy Ilanga was ordered by the rebel leadership to be the newcomer's interpreter since Guevara could not speak Swahili or any of the local Congolese languages.
As a military mission, the Cuban adventure in eastern Congo was, as Che Guevara himself admitted in his diary, a failure. The idea was that a group of 100 Cubans would occupy the lakeside mountains and foment revolt.
The plan didn't take account of the fact that the level of political organisation in the Congolese rebellion was extremely weak; that Guevara and his comrades knew almost nothing about the African society they were presuming to mould; or that the pro-Western regime had the help of powerful white mercenaries.
These mercenaries, under the command of Colonel "Mad Mike" Hoare, were to chase Guevara and his men out of the Fizi Baraka mountains after just seven months of sporadic combat.
The wider picture of Cuba's involvement in Africa is quite different.
Nelson Mandela is on record as saying Cuban military and political support - notably for the anti-apartheid regime in Angola in the 1980s - was critical to the ending of white rule in South Africa.
Today, hundreds of Cuban doctors work in poor African countries. That would have pleased Guevara - and Freddy Ilanga.
During the seven months they spent together, Mr Ilanga lived and breathed Che Guevara's life.
As a young black African who saw white settlers as an oppressive force - and who knew nothing about the revolution in Cuba - Mr Ilanga was at first very wary; he once confided that he thought of Guevara as "that sarcastic white".
But he gradually grew to admire the hard-working Guevara, who, according to Mr Ilanga, showed the same respect to black people as he did to whites.
In those days, in Congo, this was truly revolutionary.
After he worked as Guevara's translator, Mr Ilanga's life changed dramatically again.
He was told to go to Havana shortly after the departing Cuban military force had left Congo in November 1965.
The official reason was that Guevara wanted him to have a decent education. But, given the tense Cold War atmosphere, the Cubans probably also had security concerns about a man who had been so close to Guevara.
When Mr Ilanga first arrived in the Caribbean he was homesick for Congo, but, after realising he would probably never get enough money together to return, he buckled down to life in Havana.
He qualified as a doctor and specialised in paediatric neurosurgery. He married a Cuban woman and had two children.
Over the years he had lost almost all contact with his family members in Africa, most of whom assumed he had been killed as a young guerrilla in the 1960s.
All that changed in September 2003 when one of Mr Ilanga's sisters-in-law, who had never given up on him, saved up to pay for a short session in an internet cafe in the city of Bukavu, near his birthplace.
She entered his name into a search engine and was astonished to see it come back on a published article signed by Mr Ilanga and marked Havana, Cuba.
Tentative approaches were made by e-mail, with neither side quite believing at first that the contact was genuine.
Freddy Ilanga then spoke by phone to his mother, Mwausi Museke, for the first time in almost 40 years.
With Katrin Hansing, Mr Ilanga began looking into ways of returning home - the principal one being to make a film of the journey, which the two hoped would finance the fares and Mr Ilanga's resettlement.
This was where I came in again, as a bit-part player; I was hoping to tag along with them to do some reports for the BBC.
Despite Freddy Ilanga's death last month, Ms Hansing still intends to complete the film.
One of her motivations is to show his family how one of their own went from being a newspaper vendor to a brain surgeon - via contact with one of the great icons of the 20th century.