Anno Domini (abbreviated as AD or A.D.) and Before Christ (abbreviated as BC or B.C.) are designations used to label or number years used with the Julian and Gregorian calendars. This calendar era is based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth, with AD counting years after the start of this epoch, and BC denoting years before the start of the epoch. There is no year zero in this scheme, so the year AD 1 immediately follows the year 1 BC. This dating system was devised in 525, but was not widely used until after 800.

Alternative names for this era include vulgaris aerae (found 1615 in Latin), "Vulgar Era" (in English, as early as 1635), "Christian Era" (in English, in 1652), "Common Era" (in English, 1708), and "Current Era". Since 1856, the alternative abbreviations CE and BCE are sometimes used in place of AD and BC.

The Gregorian calendar is the most widely used calendar in the world today. For decades, it has been the unofficial global standard, adopted for pragmatic interests of international communication, transportation and commercial integration and recognized by international institutions such as the United Nations and the Universal Postal Union.

John Henrik Clarke (January 1, 1915 — July 16, 1998), born John Henry Clark, was a Pan-Africanist American writer, historian, professor, and a pioneer in the creation of Africana studies and professional institutions in academia starting in the late 1960s.

He was Professor of African World History and in 1969 founding chairman of the Department of Black and Puerto Rican Studies at Hunter College of the City University of New York. He also was the Carter G. Woodson Distinguished Visiting Professor of African History at Cornell University’s Africana Studies and Research Center. In 1968 along with the Black Caucus of the African Studies Association, Clarke founded the African Heritage Studies Association.

Born as the eldest child 1 January 1915 in Union Springs, Alabama to sharecroppers John (Doctor) and Willie Ella (Mays) Clark. He renamed himself John Henrik (after rebel playwright Henrik Ibsen) and adding an "e" to his surname Clarke, as a symbol. Counter to his father's wishes for him to be a farmer, Clarke left Alabama in 1933 by freight train and went to Harlem, New York, where he pursued scholarship and activism.