1858: Speaking of a slave his father-in-law gave to his wife: "He is a very smart, active boy, capable of making anything... I can leave him here and get about three dollars per month for him now, and more as he gets older."(Simon, v1. p344)
The only evidence we have that Grant actually owned slaves is a certificate he signed freeing one, Wiliam Jones, in 1859. However, he certainly had control over the slaves his father-in-law gave his wife.
1878: "As soon as slavery fired upon the flag it was felt, we all felt, even those who did not object to slaves, that slavery must be destroyed. We felt that it was a stain to the Union that men should be bought and sold like cattle." (Grant, 1969, p367)
1885: "The cause of the great war of the rebellion against the United States will have to be attributed to slavery... Slavery was an institution that required unusual guaranties for its security wherever it existed; and in a country like ours, where the larger portion of it was free territory inhabited by an intelligent and well-to-do population, the people would naturally have but little sympathy with demands upon them for its protection. Hence the people of the South were dependent upon keeping control of the general government to secure the perpetuation of their favorite institution." (Grant, 1885, v2, p386)
1885: "[Before the Civil War] many educated and otherwise sensible persons appeared to believe that emancipation meant social equality. [In 1860] the Republican party was successful in electing its candidate to the Presidency. The civilized world has learned the consequence. Four millions of human beings held as chattels have been liberated; the ballot has been given to them; the free schools of the country have been opened to their children. The nation still lives, and the people are just as free to avoid social intimacy with the blacks as ever they were, or as they are with white people." (Grant, 1885, v1, 170-1)
1885: "There were people [before the Civil War] who believed in the 'divinity' of human slavery, as there are now people who believe Mormonism and polygamy to be ordained by the Most High. We forgive them for entertaining such notions, but forbid their practice." (Grant, 1885, v1, p173)
1885: "The fact is, the Southern slave-owners believed that, in some way, the ownership of slaves conferred a sort of patent of nobility -- a right to govern independent of the interest or wishes of those who did not hold such property. They convinced themselves, first, of the divine origin of the institution, and, next, that that particular institution was not safe in the hands of any body of legislators but themselves." (Grant, 1885, v1, p 180)
1885: "The [South] was burdened with an institution abhorrent to all civilized people not brought up under it, and one which degraded labor, kept it in ignorance and enervated the governing class... Soon the slaves would have outnumbered the masters, and, not being in sympathy with them, would have risen in their might and exterminated them. The war was expensive to the South, as well as to the North, both in blood and treasure, but it was worth all it cost." (Grant, 1885, v1, p507-8)