|Reference style||The Most Reverend|
|Spoken style||His Excellency|
|Posthumous style||not applicable|
Matthiesen was born in Olfen, Texas. He was ordained to the priesthood on March 10, 1946. On March 18, 1980, Matthisen was appointed bishop and he was ordained on May 30, 1980. He retired on June 21, 1997.
He was notable for pursuing controversial causes within the concerns of Catholicism, including a stay of execution for the killer of a nun, and providing sacramental duties for homosexuals, as well as for influencing the resignation of Catholic workers at the Pantex plant in the 1980s. Matthiesen has been in the news recently for advocating increased benefits for certain former priests from his diocese, that have been defrocked due to allegations of sexual misconduct.
Facing budget cuts, recently the Amarillo diocese slashed the stipend payments for ousted priests from $1600 to $100 USD. Reacting on what he considers a moral obligation, Matthiesen seeks to provide aid to three priests, Dennis Boylan, John Salazar, and Jim Hutzler.
He won the 2009 Pax Christi USA Teacher of Peace Award.