When was it invented

[jettyjockey18]

this is straight from Lunker City's website...

History of Slug-Go®
As hard as it is to believe today, prior to the mid-1980s, there was no such thing as a 'soft stickbait' or 'soft jerkbait'. Back then, Lunker City Fishing Specialties occupied Herb Reed's garage, and supplied a small group of avid anglers with custom-built spinnerbaits (Thunder Blades), living rubber jigs (Jungle Jigs) and hand poured soft plastic lures in color patterns that at the time, were considered exotic. The soft-stickbait concept germinated when Reed connected a few common bass fishing observations...

... Slug-Go® actually won its first tournament in May of '87, at Lake Winnepesaukee, when Reed and partner Phil Hunt Slug-Goed a limit of smallies that averaged nearly 5 pounds apiece. By 1988, the lure had become the 'secret weapon' of a handful of avid northeastern bass anglers. In 1989/90 Slug-Go was the subject of feature articles in In-Fisherman and BASSMaster magazines. 5th and 2nd place finishes in B.A.S.S. Invitational tournaments in the '90-'91 season helped secure Slug-Go®'s place in history. Within a year, it had become the hottest selling new soft plastic lure introduction in bassing history...