Question: The father of Grinnell Willis was once the employer of which former slave and future writer?

Context paragraphs:
Mahommah Gardo Baquaqua: Mahommah Gardo Baquaqua was a former slave, native of Zooggoo, West Africa, a tributary kingdom of Bergoo kingdom.  He worked in Brazil as a captive, however he escaped and fled to New York in 1847, assuring his freedom.  He wrote a biography, published by American abolitionist Samuel Moore in 1854.  His report is the only known document about slave trade written by a Brazilian former slave.

São José Paquete Africa: The São José Paquete Africa (also, "São José-Paquete de Africa") was a slave ship from the Kingdom of Portugal that sank in 1794 off the coast of Cape Town, South Africa.  Close to shore, but in deep water, 212 of the 400 to 500 African slaves who were aboard died when the ship sank.  In 2015, the Smithsonian's African American History Museum, South Africa's Iziko Museums, the Slave Wrecks Project, and other partners, confirmed discovery of the wreck near where it sank.  The ship and its slaves were headed from Portuguese Mozambique to Colonial Brazil, during the height of the international African slave trade.  Few other former slave ships have been found, but the "São José" is the first and only shipwreck discovered, as of June 3, 2015, of a working slave ship, which sank in transit with its human cargo aboard.

Grinnell Willis: Grinnell Willis (1848-1930) was a textile merchant and philanthropist, and the son of noted poet Nathaniel Parker Willis.  Willis founded and ran Grinnell Willis & Company.  He also funded several civic projects in the Morristown, New Jersey area.

First Servile War: The First Servile War of 135–132 BC was an unsuccessful slave rebellion against the Roman Republic.  The war was prompted by slave revolts in Enna on the island of Sicily.  It was led by Eunus, a former slave claiming to be a prophet, and Cleon, a Cilician (from present-day Turkey) who became Eunus's military commander.  After some minor battles won by the slaves, a larger Roman army arrived in Sicily and defeated the rebels.

James Augustine Healy: James Augustine Healy (April 6, 1830 – August 5, 1900) was an American Roman Catholic priest and the second bishop of Portland, Maine; he was the first bishop in the United States of any known African descent.  Born in Georgia to a mixed-race slave mother and Irish immigrant father, he identified and was accepted as white Irish American, as he was half Irish and majority European ancestry.  When he was ordained in 1854, his mixed-race ancestry was not widely known outside his mentors in the Catholic Church.  (Augustus Tolton, a former slave who was publicly known to be black when ordained in 1886, is sometimes credited as the first black Catholic priest in the U.S.)

Nathaniel Parker Willis: Nathaniel Parker Willis (January 20, 1806 – January 20, 1867), also known as N. P. Willis, was an American author, poet and editor who worked with several notable American writers including Edgar Allan Poe and Henry Wadsworth Longfellow.  He became the highest-paid magazine writer of his day.  For a time, he was the employer of former slave and future writer Harriet Jacobs.  His brother was the composer Richard Storrs Willis and his sister Sara wrote under the name Fanny Fern.

Ignatius Sancho: Ignatius Sancho (c. 1729 – 14 December 1780) was a British composer, actor, and writer.  He is the first known Black Briton to vote in a British election.  He gained fame in his time as "the extraordinary Negro", and to eighteenth-century British abolitionists he became a symbol of the humanity of Africans and immorality of the slave trade.  "The Letters of the Late Ignatius Sancho, an African", edited and published two years after his death, is one of the earliest accounts of African slavery written in English by a former slave of Spanish and English families.

Harrison Barrett: Harrison Barrett (1845 – 1917) was a former slave born in 1845 to slave parents from Louisiana, Simon and Eliza Barrett.  He had two brothers and two sisters.  After the emancipation of the slaves in 1865, Barrett searched for his family members.  He was able to gather all together except for one sister.  In 1889 he purchased land east of the San Jacinto River in Harris County, Texas, for fifty cents an acre, and named the area Barrett Settlement.  It was one of the largest holdings in Harris County to be acquired by a former slave.  He is interred with his wife Annie Jones Barrett, along with four other family members, in the nearby cemetery.

Jordan Anderson: Jordan Anderson or Jourdon Anderson (December 1825 – April 15, 1907) was a Black-American former slave noted for a letter he dictated, known as "Letter from a Freedman to His Old Master".  It was addressed to his former master, Colonel P. H. Anderson, in response to the Colonel's request that Mr. Anderson return to the plantation to help restore the farm after the disarray of the war.  It has been described as a rare example of documented "slave humor" of the period and its deadpan style has been compared to the satire of Mark Twain.

Matson Trial: The Matson Trial (1847), officially Matson v. Ashmore et al. for the use of Bryant, was a freedom suit by former slave Anthony Bryant on behalf of his family in Coles County, Illinois.  It is noted for the unusual circumstance where Abraham Lincoln, the future emancipator of slaves, defended a slave-owner against a slave.  The case pitted Lincoln and former Illinois Attorney General Usher F. Linder against former US Representative Orlando B. Ficklin.  Ficklin's case proved successful, and Bryant's family was emancipated based on free soil doctrine.

Supporting paragraphs: Grinnell Willis Nathaniel Parker Willis
Answer: Harriet Jacobs