His best-known film acting roles are as Egon Spengler in `` Ghostbusters '' ( 1984 ) and Russell Ziskey in `` Stripes '' ( 1981 ) ; he also co-wrote both films .
His best known movie roles were as Egon Spengler in `` Ghostbusters '' ( 1984 ) and Russell Ziskey in `` Stripes '' ( 1981 ) , both movies he co-wrote .