Gendry is the bastard son of King Robert Baratheon although he didn't know of his origin until Stannis Baratheon and Melisandre tried to use his royal blood for a mystical spell. After escaping their clutches and returning to King's Landing, Gendry forged a weapon for himself: a hammer inspired by the Warhammer swung by his father in the days of old. Eventually, Gendry joins Jon Snow's expedition north of the Wall to capture a wight as an example of why the Seven Kingdoms must unite against the Night King. This is the mission where we see Gendry's hammer in action, successfully smashing several wights to smithereens.
As a blacksmith by trade, we expect Gendry to fire up the forges of Winterfell in season eight to craft weapons (hopefully of Valyrian steel!) suitable for use against the undead.