YouTube Star Steph Pappas' Father Killed by Suspected Drunk Driver

Steph Pappas' father was killed by a suspected drunk driver in Ohio this weekend -- and her mother was also injured ... this according to law enforcement.

John Pappas was pronounced dead on the scene Sunday night in Stark County after he and his wife, Kristine -- both parents to the 22-year-old YouTube star -- were struck by a driver traveling westbound ... who cops say veered into the Pappas' vehicle.

Jackson Township PD tells TMZ ... the driver is believed to have sideswiped the Pappas' car after veering off the centerline, and that there was heavy damage to the driver's side door.

First responders rushed to the scene, but officials from the Coroner's Office found John had succumbed to his injuries. Kristine was rushed to the hospital -- her condition is unknown.

Cops are saying drugs and/or alcohol are believed to be a contributing factor to the crash, however ... no arrests have been made yet. Jackson Township won't tell us what obvious signs of impairment they observed, but they do say they're investigating and collecting samples to present to prosecutors ... which they believe will lead to criminal charges.

Steph has a massive following as an up-and-coming influencer -- she has 1.4 million subscribers and hundreds of thousands of IG followers as well. She's acknowledged her father's passing online, saying she "wants my dad back."

Other influencers, like Shane Dawson, have sent their condolences.

John was 53.