25. Benjamin Banneker

Notable invention: The U.S. wooden clock

The son of a slave, Banneker developed a fascination for repairing watches by taking them apart and studying their components. After mastering his craft he would go on to build America's first-ever wooden clock using carved wooden pieces. The clock worked for more than 40 years. Banneker banked on his nationwide exposure and started up his own watch and clock repair business. They don't make them like they use to.