Pegasus was published from 1981 to 1983 by Judges Guild. It replaced the Dungeoneer’s Journal magazine, running for 12 issues, from 1981-1983. Issue 13 was created but never released. When Judges Guild returned in 1999, issues 14 & 15 were published.
More info here:
http://mboone.tripod.com/jg_pegasus.html