John Francis Lewis Jr., 49, of San Antonio, was killed about 2:25 a.m. just inside the north part of the Live Oak County line, according to Sheriff Larry Busby.
Busby said witnesses said Lewis was seen in the southbound lanes traveling north.
"Lewis struck a parked vehicle on the side of the road, spun around and came to a stop. He got out and was wandering around," Busby said.
Other drivers stopped and yelled at Lewis to get out of the road. But then an 18-wheeler struck him.
Lewis was driving a 1995 Ford pickup. The vehicle was registered to Lewis.
Busby said a driver on I-37 earlier at about 12:45 a.m. reported a vehicle traveling south in the northbound lanes of I-37 at the south end of Live Oak County.
"The driver gave a vehicle description that matched the later accident," Busby said.
But the driver took the Mathis exit and was not seen or heard about again until the fatality was reported.
Live Oak County justice of the peace Endercio Chapa filed the inquest.
In addition to the Live Oak County Sheriff's Office, the Three Rivers Volunteer Fire Department, Three Rivers Police Department and the Department of Public Safety responded the accident.