Answer
Desmond Leslie co-wrote Adamski's book'Flying Saucers Have Landed', which was a bestseller in the 1950s. Leslie had met Adamski in 1952 and the two men had become close friends. Leslie was a supporter of Adamski's claims about flying saucers and he helped to promote the book. The book was a success and it helped to popularise the idea of extraterrestrial life.