As the axis of the Earth oscillates slowly during precession, the north pole of the planet points towards different places of the sky at different times. As such, the current North Star, Polaris, may not bear this label for long, in terms of astronomical timing.
 

Common knowledge says that the North Star is the brightest in the sky and it is situated directly overhead, straight above its potential viewers. This is a double mistake, since Polaris is quite far from being the brightest star (it's only the 49th brightest, actually), and it is not located straight above, except when observed from the North Pole. The shiniest observable star title actually belongs to Sirius.
 

Earth's axis oscillates during the ever changing precession of the equinoxes (the rotational motion of Earth's axis, similar to a spinning top), tracing out a conical form in the sky along a cycle that lasts for about 26.000 years. This cycle, also known as the Great Year or the Platonic Year, is a crucial factor in determining the length of an astrological age. The precession movement is mainly influenced by the Sun and the Moon's gravity forces exerted on the equator.
 

As previously said, the North(ern) Star is the prominent star that appears (approximately) straight overhead to a North Pole-based viewer, since it's located closest in the sky to the northern celestial pole. The actual North Star, Polaris, is part of the Ursa Minor constellation found at the end of the Little Dipper asterism (a pattern of stars that is not a constellation in itself) and has been used in old navigation orienting systems for a long time. This orientation process was based on the fact that, with the horizon, Polaris forms and angle equal to the latitude of the observer. But this could only be applied for the sailors of the northern hemisphere, as that is the only place from where the star is visible.
 

Since the Platonic Year is so long, a North Star gets to keep its title for many centuries. Polaris was preceded in this regard by the faint Thuban from the Draco constellation, shining with only one fifth of the brightness of Polaris, which claimed Thuban's crown as the northernmost star in 3000 BC. It will have to pass it on, though, about 1000 years from now, to Gamma Cephei (or Alrai, located 45 light years away), which is going to be closer to the north pole axis than Polaris. In fact, the closest it'll get will be in about 4000 CE. The next in line is Iota Cephei (or ι Cephei, found at 115 light-years away from Earth) approximately 5200 CE. It is only around 14000 CE that the first magnitude star, Vega (26 light years away), will become our North Star. Hopefully, there will be someone left to watch it from Earth.