Marcian David (Matty) Bleahu (14 March 1924, in Brașov – 30 July 2019, in Bucharest) was a Romanian geologist, speleologist, geographer, alpinist, explorer, writer and politician. He is well known for his scientific contributions to the development of the theories of global tectonics (applied to the study of the geology of the Carpathian Mountains), for his pioneering in speleology and for the development of this science, but also for the popularization of science and of ecology in Romania.
Bleahu was the author of more than 41 books and 126 scientific papers, of more than 400 articles on different topics. He had more than 500 public appearances as a speaker, including the radio and the television; he was a pioneer in using the multimedia in conferences and was the author of the first geological map of Romania. As such, Bleahu was one of the most important Romanian scientific personalities of the second half of the last century. His books and his conferences have inspired generations of youth fond of nature, mountains, the exploration of the caves in Romania, and he has been, at the same time, a mentor for many Romanian geologists after the Second World War.