Nov 26 (Reuters) - Broadway composer and lyricist Stephen Sondheim, who helped American musical theater evolve beyond pure entertainment and reach new artistic heights with such works as "West Side Story," "Into the Woods" and "Sweeney Todd," died early Friday at the age of 91, his publicist said.

"Hamilton" creator Lin-Manuel Miranda, who was in turn mentored by Sondheim, has called him musical theater's greatest lyricist.

Sondheim's most successful works included "Into the Woods," which opened on Broadway in 1987 and used children's fairy tales to untangle adult obsessions; the 1979 thriller "Sweeney Todd," about a murderous barber in London whose victims are served as meat pies; and 1962's "A Funny Thing Happened on the Way to the Forum," a vaudeville-style comedy set in ancient Rome.

"I love the theater as much as music, and the whole idea of getting across to an audience and making them laugh, making them cry - just making them feel - is paramount to me," Sondheim said in a 2013 interview with National Public Radio.

Actress Bernadette Peters, who played the roles of Dot and Marie in "Sunday in the Park" and the witch of "Into the Woods," expressed sadness at the loss of a friend, tweeting, Sondheim "gave me so much to sing about.".

Fellow actress Anna Kendrick, who starred as Cinderella in the film version of "Into the Woods," called Sondheim's death "a devastating loss.".

As Sondheim collected accolades, New York City's Broadway theater industry underwent many changes.

But Broadway musicals also became more artistic, and Sondheim played a key role in their evolution, critics said.

Hammerstein, who along with composing partner Richard Rodgers created the classic musicals "Oklahoma!" "South Pacific and "The Sound of Music," taught the teenage Sondheim how to write musical theater

After Sondheim became famous, he mentored others on Broadway

When Miranda began work on a rap musical about American founding father Alexander Hamilton, Sondheim encouraged and critiqued him