It depends on what website you visit. Wikipedia says he's an independent; even color codes him that way in their page for order of succession to the presidency. But the Notable Names Database still lists him as a Republican.
She does not belong to any party, her office is independent of political affiliation.
Robert Gates is not registered under any particular political party, but he considers himself a republican.
Ulysses S. Grant was in the Republican party.
He is an independent candidate for President of the United States
As far as I understand he didn't belong to a political party, and what party he would belong to would depend on what country you are in, but if he did have a political affiliation he would be on the far right with the people who believe that a single entity should rule over all.
Robert James Lee Hawke belonged to the Australian Labor Party
Sojourner Truth did not belong to any political party. She was a prominent African American abolitionist and women's rights activist who fought for the rights of all people regardless of political affiliation.
Democratic
Republican Party
Bill Gates' exact political affiliation is unknown. He seems to favor whatever party, at the time, is better suited to his corporate goals. Since 1999, he has donated money to both the Republican and Democrat parties at a ratio of 54% Democrat and 46% Republican.
Democratic party
Democratic Party. One of the two major political parties in the US.