My friends and I were conversing on Team Speak we all came upon this question. Is it even mentioned in the books? I know that he was important in the way of knowing White Walkers can be slain, but I am asking if he was of high-rank, or if he was known in a behind the scenes plot of something bigger in say, the current book?
There's no canon explaining White Walkers, whether they have a society, how it functions etc. The only things we know are things that we've seen, such as that they turn dead humans into Wights, and they can be harmed by Dragonglass/Obsidian, and by Valyrian steel. Anything else is just rumours and stories by people in Westeros, such as Old Nan.
According to Melissandre, the White Walkers worship a god known as the Great Other. The only source for this is Melisandre, so it's certainly not given as fact. However considering the things we've witnessed from her (and Thoros/Dondarrion), and the fact that the series is titled A Song of Ice and Fire, I'm inclined to believe that she is correct. So assuming that she is, this would suggest that the White Walkers do have some sort of society, so there may be some form of hierarchy amongst them. As to whether or not the White Walker in question is of importance, that's impossible to say.
So in short, no we don't know anything about White Walker society and hierarchy; so we don't know whether the one in question was considered important.
Update based on season 4, episode 4
In this episode, something is revealed that isn't yet written in the books. Baby boys (human) are turned into White Walkers by an unknown White Walker, who is believe to be the Night's King due to a possible spoiler from HBO. There's a number of things we can glean from this, which should give us more information.
Firstly (assuming that the HBO spoiler is correct) we now know that the White Walkers have a king, and therefore a hierarchy. Whilst we still can't be certain, we can draw parallels between them and us. Considering that the White Walker that encountered Samwell Tarly was alone, when enemies were nearby, then we can assume that it wasn't high ranking. A King, Lord, General or other does not go out scouting alone. So it's likely that this particular White Walker was a scout, or something like a soldier (or perhaps even operating alone; we don't yet know if the White Walkers are all unified).
However if all White Walkers come from human babies, then it stands to reason that there numbers won't be very large (this also makes sense with why they haven't been more brazen with their attacks; and why they convert wights). So in this regard, I'd say all White Walkers are important to them, as they don't have sufficient population numbers to afford to lose many.
So to summarise my hypothesis, I'd say that they are important due to their low population size, but not high-ranking within their hierarchy/society; probably a scout or something similar.