Critical Jack originated in Spain, where breeder Dinafem Seeds pollinated their own Critical + (or Critical Plus) with a Jack Herer male from Sensi Seeds to form this high-yielding, resin-coated, fruity-flavored bud.

This strain tends to produce a long-lasting balance of an energizing head buzz and warm, relaxing body effects, and according to Dinafem Seeds, the aroma of Critical Jack consists of hints of wood, incense, pine, spices, and lemon. The strain won first place for Outdoor Sativa at the 2016 Unión Cannábica Latino Americana Cup, and first Place for Best Shatter at the 2015 San Bernardino, California, Hempcon Cup.