Lowell Gilmore plays artist Basil Hallward
text from Wikipedia:
The painting entitled Picture of Dorian Gray used in the film was painted on commission during the making of the film in 1943-1944 by Ivan Le Lorraine Albright, an American artist who was well-known as a painter of the macabre. Created specifically for use in the film, it is now part of the art collection of The Art Institute of Chicago. Albright had to paint the picture while the movie was being made in order to show Dorian Gray's physical transformation as his evil actions changed him into a horrid image in the painting while his actual physical appearance remained that of a young man. At the film's climax, Gray "killed" the painting by piercing it through its heart with a knife, thus killing himself when his physical appearance changed to that of the painting.
The Picture of Dorian Gray on IMDB