Sidhu Jetha, also known as Siddheshwar Bose, is a character in the Feluda series who is Feluda's uncle and a close friend of Feluda's father. He is a bibliophile and has a vast knowledge of current and historical affairs. He is known for his photographic memory and is a source of information for Feluda. It is believed that the character is based on Nirmal Chandra Kumar , the antiquarian. Nirmal Chandra Kumar, my father was an antiquarian. He had a large collection of books, maps, prints in his collection, through which he delved throughout the day. His friends, Satyajit Ray, Radha Prasad Gupta, Subho Tagore, Shanti Chowdhury, Vasant Choudhuri and others visited him for a session of ‘adda’ in the evening where books, among other subjects were discussed.
When Satyajit Ray, the famous filmmaker, started his research on the mutiny for his film Satranj ki Khilari (The Chess Player), he depended on Kumar for rare books on the subject. Kumar not only provided him all the relevant books, but also went out of his way to bid for a Scrap Book, in a London Auction, on Mutiny, having paper clippings and notes on the historic happening. Ray did not forget this gesture and the fact that Kumar had always helped him with innumerable information and facts, leave aside the many antique props for his sets and paid him his biggest personal tribute. He based one of his characters in his story book series on Feluda, the detective etched on Kumar. Sidhu Jaytha (Sidhu Uncle) in the Feluda series, with an encyclopaedic knowledge immortalizes Kumar, who had a vast knowledge on many subjects.