Perry Rhodan is the name of science fiction series published since 1961 in Germany, as well as the name of the main character. Perry Rhodan is a space opera, dealing with several themes of science fiction. Having sold over one billion copies (in pulp booklet format) worldwide, it is the most successful science fiction book series ever written. The series and its spin-offs have captured a substantial fraction of the original German science fiction output and exert influence on many German writers in the field. The series is told in an arc storyline structure similar to that later used by Babylon 5. An arc (called a "cycle") would have anywhere from 25 to 100 issues devoted to it, similar subsequent cycles are referred to as a "grand-cycle".