The word "nigger" originated as an adaptation from several languages and ultimately traces back to the Latin adjective "niger," meaning "black." It was initially borrowed into English in the 16th century from French "nègre," which itself came from Spanish "negro," both meaning "black." The earliest English forms were spelled "neger" or "niger." The word started as a relatively neutral term referring simply to a dark-skinned person. The first known English use dates from 1574. Over time, especially by the mid-18th century and into the 19th century, the word took on a derogatory meaning in the context of racial slavery and oppression in America. The transition from a color descriptor to a racial slur was closely linked to the system of African slavery in America. The word's shift into a pejorative epithet was well established by the early 1800s. Variants like "niggor" appeared in records as early as 1689 in Brooklyn, New York. The word "nigger" thus evolved over centuries from a Latin term for black to a deeply offensive racial slur through usage patterns in colonial and American English influenced by racism and slavery.
In summary, the "inventor" of the word in the modern derogatory sense is not attributable to a single person but rather is the result of linguistic evolution starting from Latin through French, Spanish, and English colonial contexts, especially connected with racialized slavery in America.