James Dominic Fenix, better known as JD Fenix or J.D. Fenix, is a fictional character in the Gears of War franchise. The son of recurring series protagonist Marcus Fenix, he first appears as the protagonist of the 2016 game, Gears of War 4, and also appears in Gears 5. Prior to the events of Gears of War 4, he originally held the rank of lieutenant in service of the supranational and intergovernmental military collective known as the Coalition of Ordered Governments ("COG"), and later defected to a loosely organized faction of rebel human settlers who live outside of the COG's walled settlements in the world of Sera. By the events of Gears 5, he has rejoined the COG to fight a new threat to humanity. The character is voiced by Australian actor Liam McIntyre. Outside of the video game series, JD has appeared in the novels Gears of War: Ascendance and Gears of War: Bloodlines.

The concept of JD as a character originated when series creator Epic Games was still in early development for a direct sequel to Gears of Wars 3. The Coalition, a subsidiary of Xbox Game Studios and the current developers responsible for the Gears of War franchise following the departure of Epic Games from the series, intended for JD Fenix to headline a new generation of main characters introduced in Gears of War 4.

The character has had a mixed reception, with commentary focusing on his physical appearance as well as interactions with his companions. Some reviewers found JD to be an unconvincing or uncharismatic lead character and compared him unfavorably to Marcus Fenix and Kait Diaz, while his narrative role in Gears 5 has generated discussion about the future of the Gears of War franchise.