Ulysses S. Grant (born Hiram Ulysses Grant... the S stands for nothing, much like with Harry S Truman) was our 18th president.
During his predecessor's term, Grant accompanied President Johnson around the country to garner support, though Grant did not like Johnson and allied himself with the Radical Republicans for his campaign in 1868.
As former commander of all the Union armies, Grant was well-known and popular amongst the people. He also had a reputation as a very honest man, though his presidency would later be seen as rooted in scandal.
Many historians place Grant lowly amongst the presidential rankings due to what they see as an ineffectual presidency. Those who visited the White House saw Grant as weak and ineffectual, and his reputation as a drunk did not help matters. Then, his association with speculators Gould and Fisk brought him trouble, as the two sought to monopolize gold and Grant only realized and counteracted their plan after they had ruined businesses.
On top of everything, 1873 saw a worldwide depression beginning in Austria. This manifested in the USA in several ways- over-expansion of railroads and extreme speculation on the stock market brought the country into a panic.
Nevertheless, he was elected to a second term.
After all, he was quite well liked for his hardline Republican platform. He oversaw reconstruction of the South with military enforcement. He was strongly for civil rights, and he won passage of the 15th amendment that allowed African Americans to vote. The Ku Klux Klan act, also passed by him, let the Presidetn "arrest and break up disguised night marauders."
These same policies that made him popular in the North made him despised in the South. After Grant won reelection, he received notice of Southern states threatening to secede again. A relocation of troops shut down these threats.
And unfortunately, the gold fiasco was not the only scandal to plague the Grant administration. Fraud, overtaxing and bribes were common amongst big businesses, and even the Attorney General and several White House Secretaries.
He was one of a few Presidents who sought a third term, but he did not win. The presidency that year, 1880, went to James A. Garfield.
Sources: Wikipedia, Miller Center, Biography.com, The White House.gov