The North Star is a title of the star best suited for navigation northwards. A candidate must be visible from Earth and circumpolar to the north celestial pole. The current one is Polaris.
The North Star has been historically used by explorers to determine their latitude. At any point north of the equator the angle from the horizon to the North Star (its altitude) is the same as the latitude from which that angle was taken. For example, the angle to the North Star for a person at 30° latitude will be about 30°.
Polaris has a visual magnitude of only 1.97. On the other hand, in 3000 BC the faint star Thuban in the constellation Draco was the North Star; and at magnitude 3.67 it is five times fainter than Polaris. The bright Vega will be the North Star by AD 14,000. In comparison the brightest star, Sirius, has a magnitude of −1.46 (assuming that we exclude the Sun at −26.8).
Currently, there is no South Star as useful as Polaris; the faint star σ Octantis is closest to the south celestial pole. However, the constellation Crux, the Southern Cross, points towards the south pole.