If you are searching for historical data of GNU/Linux distro, i think you might find the graphs in LinuxLinks worthed to look. It shows you a Linux distro time line from the beginning up to now (well, it's not meant to show full list of distro, since there are more than 100 of them listed in DistroWatch. I think only big distro that were listed there). I cannot put the image on this blog since it's very big (1860x1984 pixels), so i just gave you the link.
I thought that the first Linux distro was SLS, which is Slackware based on, but i was wrong. According to the graphs, it was MCC Interim which was released in early 1992 and it was developed until mid 1995. Slackware and Debian was released in 1993 (Slackware was released a bit earlier then Debian) and it's still an active distro up to now.