R Coronae Borealis (RCB) stars are the more prominent group  of high luminosity hydrogen deficient stars that are rich in carbon  and helium. They also show characteristic irregular light drops of  several magnitudes (between 3 and 8 magnitudes) at unpredictable  times, caused by expulsion of self-made clouds of dust. They range in 
surface temperatures from 4500 K to  20000 K. Some of them seem to  have made even such complex molecules like fullerenes (C60) in their  circumstellar regions. Neither their evolutionary history nor the dust 
formation mechanism are well understood. Two scenarios that have been  suggested are that the present stars are a result of merger of two  white dwarfs (CO+He) or a post born-again (AGB) giant that is  surviving after a final helium shell flash. The talk would describe  the RCB properties and highlight the problems and challenges they pose 
in understanding their origins and dust production.