The only evidence that Union general (and later United States President) Ulysses S. Grant ever owned any slaves is a document he signed in 1859 that emancipated "my Negro man William" (i.e, William Jones), whom Grant stated in the document he had purchased from Frederick Dent (his father-in-law). Little is known about William Jones; as even Grant's biographers note, "exactly when and how Grant acquired ownership of a slave remain something of a mystery." There is no other evidence showing that Grant ever owned more than this one slave, much less "several."
It is often stated that Grant's wife, Julia Boggs Dent, "owned four slaves," and Julia herself identified four "servants" whom she claimed "belonged" to her up until the end of 1862. However, those slaves had been purchased by Julia's father, Frederick F. Dent, and there is no record of his ever having transferred ownership of them to Julia — without such a transfer, neither Julia nor her husband Ulysses would have had legal authority to free them.
From 1854 to 1859 Grant managed his father-in-law's farm, White Haven, where a number of slaves lived and worked. But again, those slaves belonged to Grant's father-in-law, so Grant himself had no legal authority to set them free. (Some of the slaves at White Haven eventually drifted off during the Civil War; any that remained were freed when Missouri's constitutional convention abolished slavery in January 1865.)