"Young and artless." in the sense of being "genuine." His art was appearing artless.
"Vampires are his speciality." Er - okay.
He had success as an actor in the 1930 film Hell's Angels. The film was a major success and brought Jean Harlow to prominence, but Lyon's performance as an heroic World War I aviator was also highly regarded. For the next decade he was constantly in demand, but his popularity began to wane by the early 1940s.
By the mid-1940s he was working for 20th Century Fox. On July 17, 1946 he met a young aspiring actress named Norma Jeane Dougherty. After his first meeting with her he stated that she was "Jean Harlow all over again!". He organized a color screen test for the actress, renamed her, and finally signed her as Marilyn Monroe to her first studio contract.
Had a heart attack on the QE2 in 1979, and never made it back to shore.