4179 Toutatis is an irregular earth-crossing asteroid several kilometres in length, first observed on February 10, 1934 and then lost to astronomers for another 55 years. On its 1934 appearance it was given the appellation 1934 CT - however, when it was rediscovered on January 4, 1989 by Christian Pollas, he named it Toutatis, a Celtic tribal god who was little-known to popular culture until his appearance in the Asterix comics as the protector-deity of the lone tribe still resisting the Roman occupation of Gaul. History (or, at least, Google) does not record whether Pollas had Goscinny and Uderzo's Toutatis in mind rather than the original tribal deity; since the only fear of Asterix and the comic Gauls was that the sky might one day fall on their heads, one may suspect the former, as a humourous reference to the slim chance that one day Toutatis may crash into the Earth.
Asteroids are by convention first assigned a number, and only then, optionally, a name. The numbering system now stretches into the hundreds of thousands, with the discovery of approximately 5,000 new objects per month. Speaking roughly, the number refers to the sequence in which the asteroid's orbit is officially confirmed, rather than the sequence in which it is first discovered; this explains apparent anomalies such as the fact that the next asteroid in sequence, 4180 Anaxagoras, was discovered in 1960, 29 years earlier than Toutatis.
Toutatis is officially classified as an Apollo, Alinda and Mars-crossing asteroid. "Apollo" indicates that its orbit crosses that of the Earth, while at the same time being greater than the Earth's orbit. "Alinda" indicates that the asteroid is held in an orbital resonance with Jupiter - what this means is that Jupiter's gravity keeps on increasing its orbital eccentricity until, eventually, the asteroid has an "interaction" with an object in the inner solar system that either destroys it or changes its orbit. "Mars-crossing" is self-explanatory. What all of this means if you put it together is that 4179 Toutatis regularly approaches quite close to Earth, and has been very closely observed on several occasions, the most recent being in 2004, when its perihelion on September 29 brought it within 0.0104 AU (4 times the distance from the Earth to the moon). It will be back on November 9, 2008, when it should be approaching no closer than 0.0502 AU.
Toutatis gets called a "rubble pile" because it not really a singular object but rather a contact binary composed of two main objects with an average diameter of 4km and 2.5km respectively. It probably formed when two smaller bodies coalesced, rather than by a larger, singular object being split by an impact. It has some interesting surface features, including two impact craters roughly half a mile in diameter, and a series of ridges that some have called an "asteroid mountain range".
In addition to its complex shape, Toutatis has an irregular and highly complex "tumbling" motion which has led to some astronomers describing it as the strangest object in the solar system. It rotates with two separate periodic motions, the first of which has a period of 5.4 Earth days, the second 7.3 Earth days. The combination of these two periodic rotations results in an aperiodic "tumble" which means that its orientation in relation to the solar system never repeats. Normally, an asteroid with this kind of irregular rotation would have its motion dampened by internal friction and would lapse into a more regular rotation pattern; however, 4179 Toutatis rotates so slowly that for this to happen would take far longer than the entire lifespan of the solar system. To view an animation of Toutatis's rotation, try the following link to an AVI file: (http://reason.jpl.nasa.gov/~ostro/ToutatisHires.avi) or a MOV file (http://reason.jpl.nasa.gov/~ostro/ToutatisHires.mov).
Toutatis is an outside candidate for a future Earth-impact, due to the fact that its orbit is somewhat chaotic; the influence of the various planets it passes, and in particular the orbital resonance with Jupiter, mean that computer models cannot accurately project its trajectory further than a few hundred years from the present day. At some point it is bound to crash into something large in the inner solar system, and we will just have to hope either that it isn't us, or that by the time this becomes a real danger we will have developed a system for deflecting incoming celestial bodies. Like a great deal of the earth-crossing asteroids, Toutatis has been linked to a couple of the quatrains of Nostradamus's prophecies, and mention of it can be found on various fringe forums dealing with conspiracy theories, the end of the world, and such matters. However, as far as can be determined at the moment, we are in no immediate danger of an impact, and Toutatis is simply going to carry on swinging close by the Earth for the foreseeable future, tumbling like a potato-shaped gymnast.
References and further reading:
Asteroid Numbering: http://en.wikipedia.org/wiki/Asteroid#Numbering