Oribasius Giafranco Paolo Reuven was the personal assistant of Sigismund Dijkstra, the head of the Redanian secret service. He wrote the manuscript Shadow People, or the story of His Majesty's Secret Service, though it was later lost and remains unaccounted for.
In his later life, after the Nilfgaard-Nordling Wars, Ori was arrested, interrogated and imprisoned for six years in various prisons. Eventually he was released, however he died in a temple hospice less than a year after, likely due to the combination of his asthma, anaemia and glaucoma.
In the computer game, you can meet a bootblack in the alley outside Detective Raymond's place in the Temple Quarter. He is a good source of general information but you quickly notice that he seems rather well-informed for a bootblack. When you challenge him on this, he clams up and will not speak to you again until you have left the area completely and come back.
If you have previously engaged in a drinking contest with Thaler, you have a seemingly useless book, Shadow People, or the story of His Majesty's Secret Service. If you speak to the bootblack a second time, you will notice that you now have the option to give him a gift. Give him the book.
At this point, he says "You know who I am... ahem, I thought that scroll had disappeared for good.", which confirms that he is in fact Ori Reuven. After a bit more conversation, he gives you the Prophet Lebioda's signet ring, which will help Geralt get past Grandma at Shani's place.
Possible inconsistency's with the books Edit
Since Ori Reuven is said to spend six years in different prisons after the Nilfgaard War and the game events take place five years after the novel's ending, Ori should technically still be a prisoner and even if he was released he should be more of a human ruin, nowhere near the more or less healthy condition in which Geralt encounters him. The book about secret services is also said to be lost without a trace. It is possible however that these events happen after the game as the book did not specify when they happened, just that they did sometime in the future.