W.H.H. Hart was a practicing attorney and one of the founders of the Niagara Movement. Hart was born in Eufaula, Alabama, on October 31, 1857.
His father was Henry Clay Hart, a white slave trader born in Providence, Rhode Island, in 1829. He was a descendant of Thomas Hart, an English jurist who embarked at Baddow, Essex County, England, in the Desire, in 1635, landing at Ipswich, Massachusetts in 1639.

In 1905, Hart refused to give up his seat on a train when arriving in Maryland and move to a Jim Crow Car. For refusal to give up his seat, Hart was arrested and spent the next three days in jail. He later sued Maryland’s Jim Crow law that it should not apply to interstate travel. He won the case but was only awarded $1 in damages.

Hart enrolled in the college preparatory program at Howard University in 1876 and graduated with a Preparatory Department Certificate in 1880. He enrolled in the undergraduate program and received a Bachelor of Arts (BA) degree in 1885. He entered the Howard University School of Law and received his Bachelor of Laws (LLB) in 1887. From Howard University he also received a Master of Arts (MA) degree in 1889, and a Master of Laws (LLM) degree in 1891.

On July 11, 1905, Hart, along with twenty-eight other black intellectuals, including W. E. B. DuBois, founded the Niagara Movement with the drafting of the Niagara Movement’s Declaration of Principles. It formally incorporated in 1906 and was the precursor organization to the NAACP in 1910.

sources:

https://www.revolvy.com/page/William-Henry-Harrison-Hart