Which character popularized a crossguard-style lightsaber in the sequel trilogy?

In The Force Awakens, the sequel trilogy’s central dark-side antagonist debuts an unstable, red blade with blazing side vents that form a crossguard. Those “quillons” act as exhaust ports for a cracked kyber crystal, stabilizing the volatile plasma and offering hand protection and grappling options, evoking a medieval broadsword look. The design drew on ancient lightsaber variants seen in lore, but this portrayal made it iconic for modern audiences. The distractors don’t fit: Kamino is a stormy ocean planet known for cloning; Ki-Adi-Mundi is a Cerean Jedi Council member who uses a conventional blue saber; and K-2SO is a reprogrammed Imperial security droid from Rogue One, not a Force user and never a lightsaber wielder.