Googled terms: Radu Negru/Negru Vodă + legend + mythology + history of Wallachia + Romanian mythology + Romanian legends etc. in various permutations and in three different languages, none of which is Romanian
Unfortunately, there's not much info to be found, apart from the fact that Radu Negru was the legendary founder of Wallachia. The "legendary" aspect suits me very well, but I'd like to use as many established mythological "facts" as possible, if such facts exist at all.
What I have found out is that Radu Negru is a conflation of later rulers of Wallachia, and that legend has it that he came over the Carpathian mountains, founded and ruled Wallachia and built churches in Câmpulung and Curtea de Argeş. I would like him to come to Wallachia with Transylvanian Saxons and Székely people in his entourage.
What I am looking for is input from Romanian speakers and people familiar with the legend. Are there any specific myths associated with Radu Negru? What do the legends that surround the foundation of Wallachia say? Did he for example bring a holy relic over the mountains that was venerated at the first church he built? Any little titbit would be very helpful, because non-Romanian sources are not very forthcoming.