Oribasius Giafranco Paolo Reuven, better known as Ori Reuven, was the personal assistant of Sigismund Dijkstra, the head of the Redanian secret service for 19 years. 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 second Northern War, he 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 later, 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.
- There are a few inconsistencies between his character in the books versus the games. In the games, he'd have likely been in prison when Geralt visited Vizima. His book was also lost without a trace while in the games one can be given a copy.
- It should be noted though that is is only based on him being arrested soon after peace was declared. The books don't specifically state when it all happened.