why is it called the mandela effect

It is called the "Mandela Effect" because the term was coined by paranormal researcher Fiona Broome after she and many others shared a vivid but false memory that Nelson Mandela had died in prison in the 1980s. In reality, Mandela was released from prison in 1990, went on to serve as president of South Africa, and died in 2013. This widespread false memory phenomenon led Broome to create a website to discuss similar shared false memories, and the name "Mandela Effect" stuck to describe such collective memory errors.