Fasching, who graduated from Saint John's in 1981, has been an assistant at the school for the past 17 years.
John Gagliardi retired as head coach after the 2012 season, having been at Saint John's since 1953. Prior to that he coached at Carroll College in Montana.
His 489 victories are the most for any head coach in college football. Both Saint John's and Carroll College are Division III NCAA programs.
During Fasching's time as an assistant coach, Saint John's posted a 164-39 record with one national championship and one national runner-up effort.
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