Brandon Gullickson was hit Saturday night on the Fraser Highway at 176th Street. Police say another car crashed into Gullickson, pinning him under the vehicle.
His girlfriend, Cassy Dryden, was also seriously injured, but it's unclear how.
RCMP Cpl. Bert Paquette says it's too soon to say if speed or alcohol were factors, or if charges will be laid.
"The Good Samaritan, as far as we know, suffered significant injuries and is in critical but stable condition in hospital at this time," he said.
Friends have set up an account at the Bank of Montreal to help pay for the couple's medical expenses.
Photos of the couple in hospital were posted to a Facebook page called the "Cassy Dryden and Brandon Gullickson Fund" on Tuesday.
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