American blacks have always been a self-defining people. There are instances of African slaves being whipped and beaten because they defiantly rejected the English, Portuguese, French and Spanish surnames imposed on them, as documented in Alex Haley’s Roots.
It was a common practice for slaves – if they used or were allowed last names at all – to use the family name of whatever slaveholding family happened to own them. It was common practice for such slaves to have their last names changed as they were sold to master to master.
DelawareEng. When slaves took their own identities, it was by personal choice and an informal matter unregulated by government. This is one of the reasons why family Bibles are still acceptable proof of identity and family lineage.
What Otto said about freed slaves adopting presidential last names is true, but that tended to happen en masse among the newly emancipated slaves in the immediate aftermath of the Civil War.
SHAKES. Many, many slaves however, especially those who continued to sharecrop on their master’s property after being emancipated, tended to keep their master’s last names as pass it on to their children, especially if they used it since birth.
Later in the 20th century beginning in the last 1940s, when the possibly apocryphal W.F. Fard began the Islamic sect The Nation of Islam that many American blacks – enthralled by his bizarre gospel of white devil white men reversed-bioengineered by mad Dr. Yacub – began to adopt Islam as their religion and reject any form of of their "slave names’, including a “slave diet” of kale, collard greens, mustard greens, etc, – although this last stricture has been largely relaxed by many black American Muslims in the last few decades. Prominent American black Muslims are probably already known to you, but they include sports figures like the former Cassius Clay, Muhammad Ali and Lew Alcindor, Kareem Abdul Jabbar and Malcolm Little – Malcolm X, later El Hajj Malik El Shabazz. Activist Stokeley Carmichael famously changed his name to Kwame Toure
Later still, in the 1960s and 70s, it was the vogue for African culture among some American black youth that prompted them to assume African and faux-African identities, particularly first names for themselves and their children, which is how I got the name Askia Moshe Kinshasa… Many people also got matching last names, too: Dr. Maulana Karenga, inventor of the African American holiday of Kwanzaa, was born Ron N. Everett, son a Baptist minister. NAACP president Kweisi Mfume was born Frizzell Gray.
An interesting aside – among native Africans the reverse is trie – many Christian Africans with Biblical and English first names and tribal ethnic last names are now adopting African cultural first names, the reverse of the African-American experience.
Then there’s the whole stage name phenomenon of many rappers and hip-hop artists like the individual members of the Wu Tang Clan, Outkast, Ludacris, etc.