At key moments in his adolescence, Barack Obama could not turn to a father he hardly knew. Instead, he looked to a left-leaning black journalist and poet for advice on living in a world of black and white.

Frank Marshall Davis had his opinions. He once argued that the public schools of his youth prepared neither blacks nor whites for "life in a multiracial, democratic nation." He called hypocrisy "a national trait of American whites." Advocating civil rights amid segregation, Davis wrote in 1949: "I refuse to settle for anything less than all the rights which are due me under the Constitution."

The depth of the influence Davis had on the presumptive Democratic nominee is a question. While Davis' leftist politics could allow the candidate's critics to group Davis with Obama friends and acquaintances with allegedly anti-American views, those who knew Davis and his work say his activism was aimed squarely at social injustice.

Obama's father was a black man from Kenya and his mother a white Kansas woman. They separated when Obama was 2, and he saw his father just once after they divorced two years later. Raised with the help of his white grandparents, Obama attended school in his native Hawai'i with few black peers. He struggled to find mentors in his search for a black identity.

His white grandfather, Stanley Dunham, was friends with Davis — both had roots reaching back to Kansas and had families of mixed races — and the black writer took an interest in Obama.

"Our grandfather ... thought (Frank) was a point of connection, a bridge if you will, to the larger African-American experience for my brother," Maya Soetoro-Ng, Obama's half-sister, said during a recent interview.

Although Davis does not appear to have been a constant figure in his early life, Obama in his 1995 memoir, "Dreams from My Father," presents Davis — referred to in the book only as Frank — as an important influence who gave him advice about race and college.

A longtime journalist, Davis (1905-1987) was among a group of prominent black writers pushing for equal rights in the 1930s and '40s, before the civil rights movement gained momentum. He published several volumes of poetry and served as executive editor of the Associated Negro Press, a wire service for black newspapers, before leaving the Mainland for Hawai'i in 1948.

"Frank was part of a group of black vanguard intellectuals," said Kathryn Takara, a professor emeritus at the University of Hawai'i who wrote her Ph.D. dissertation about Davis. "The people that he came into contact with throughout his life, like Richard Wright and Margaret Walker, were very significant."

As a young man in Kansas in the early part of the 20th century, Davis encountered segregation and racial epithets. In his memoir, "Livin' the Blues," Davis describes almost being lynched by a group of his white schoolmates as a 5-year-old in Arkansas City, Kan.

"You could get a lot of strength from a person like Frank who had suffered all the discrimination ... that a black man goes through in America," said Ah Quon McElrath, a friend of Davis' who lives in Honolulu.

Davis scholars dismiss the idea that he was anti-American.

John Edgar Tidwell, a University of Kansas professor who wrote the introduction to Davis' memoir and edited a collection of his work, declined by e-mail an interview request, saying Davis has become the victim of a "McCarthy-era strategy of smear tactics and condemnation by association."

In his introduction to "Writings of Frank Marshall Davis: A Voice of the Black Press," Tidwell wrote of Davis and his later work: "He made his vision into a beacon, a light shedding understanding and enlightenment on the problems that denied people, regardless of race, national origin or economic status, their constitutional rights."

For Obama, Davis was an intriguing figure, "with his books and whiskey breath and the hint of hard-earned knowledge behind the hooded eyes."

Dunham and his grandson would spend evenings at Davis' dilapidated home in Waikiki. Davis, who had raised a family with a white wife, would read his poetry and share whiskey with Dunham, Obama recalled.

Dawna Weatherly-Williams, a friend of Davis' who also lives in Honolulu, said Dunham wanted Obama to know that there were other children like him who were part black and part white, she said.

"Stan was real proud of that," she said, adding that it was rare to see black men with white women at the time.

Obama describes driving to Davis' home in Waikiki after learning his white grandmother was so afraid of a black panhandler she did not want to take the bus to work. Davis told the teenager that his grandmother was correct to feel scared because she understood blacks "have a reason to hate."

Davis said Obama's grandfather would never understand people like him because they hadn't experienced the humiliations he had, according to Obama's memoir. As he left Davis' house that night, Obama wrote, he knew he was completely alone for the first time in his life.

Davis appears again later in the book, when Obama recalls meeting the writer shortly before leaving for college on the Mainland. At that meeting, Davis scolded Obama for his listless attitude toward college and warned him not to leave his race behind, which he called "the real price of admission" to higher education. Davis went on to tell Obama that no matter how well he did in college, his race would be a glass ceiling.