Millard Fillmore is another of those lesser known presidents. He was the second of currently twelve presidents who held office without a vice president. He switched during his life from the anti-Masonic party to the Whig party, and he rose to the presidency following Zachary Taylor's death, as he was Taylor's vice president.
One of the things Fillmore should be known for is his foreign policy. It was due to his influence that Japan was forced to open up and trade with the Treaty of Kanagawa. He also aggressively protected territories from the Americas from foreign control, such as opposing French attempts to annex Hawaii and French and British attempts to invade Cuba. He also later switched to the Know Nothing party (or American party), noted for its xenophobia.
He did not slack on the home front either. He supported the Compromise of 1850 and signed the Fugitive Slave Act. When Fillmore took office, every member of Taylor's cabinet submitted their resignation. Following the bold act, Fillmore surrounded himself with fellow moderate Whigs.
After his presidency, Fillmore also detracted from Lincoln, and he supported Johnson during the Reconstruction Acts following the Civil War. Perhaps mostly due to his Southern sympathetic policies and his ideas and lax handling of the growing debate over slavery, Fillmore is consistently ranked among the ten worst presidents in US History. His popularity even during his era was not high; Whigs who felt betrayed by his protection of slavery did not support him for a second term.
Sources: Yahoo! Voices, Wikipedia, Biography.com, White House.gov