Brethauer was born to Volga German parents and grew up in Portland, Oregon.
[1] He attended Jefferson High School, where he was named first-team All-Portland Interscholastic League twice in football.
He led the team in receiving and set a school record in catches all three years.
[3] As a senior, he caught 41 passes for 486 yards and two touchdowns and was named second-team All-Pacific Coast Conference.
[6] Brethauer was drafted into the Army after the season and missed 1954 and was re-signed by the Colts after being discharged in 1955.