Not all of the stories told in "2000 AD" and its related publications exist in the same shared universe, unlike in some other comics, for example, the DC and Marvel Universes. Indeed the majority of stories which have appeared in "2000 AD" since 1977 have never been connected with each other. However, the series which are so connected are generally the most significant ones in the comic in terms of the number of issues they have appeared in, their popularity with readers, and their significance in the history of the comic.