Ulysses S. Grant led the Union Army to victory in the Civil war, and later became president. Grant was raised in an abolitionist family, but wasn't forced to attend church and remained mostly apolitical before the war. That background didn't seem to be at all strained when he married Julia Dent, who was a slave owner like her father before her, in 1848. Since Julia was a 19th-century woman, that meant that U.S. Grant was technically a slave owner. No matter who officially "owned" a household of enslaved people, Grant benefitted from their labor at his father-in-law's farm called White Haven in Missouri, where the family lived. Grant had no particular qualms against the institution of slavery, up until late in the war, when he saw it was a dying institution.
The people that Julia kept as slaves were under conflicting legal status. The Emancipation Proclamation was issued in 1863, but it only pertained to enslaved people in the Confederate states. Slave states like Missouri and Kentucky that remained in the Union were not included. Julia was under the impression that they had been freed as well, but kept them with her anyway. The enslaved people were apparently under the impression they were still enslaved. In 1864, Julia's longtime nursemaid, Jules, disappeared while traveling with Julia in Kentucky, and crossed the icy Ohio River into Indiana and freedom. The Grant's slaveholding days were numbered. Read about U.S. Grant, his wife Julia, and the people they enslaved at Smithsonian.
Also, in practical terms, the Emancipation Proclamation was political grandstanding, with Lincoln declaring slaves to be free in territory not under the control of the United States government, and over which he technically had no authority.