In a communist society, there will be no classes but in socialism the proletariat would be the ruling class. You might want to check out The State and the Revolution, avalible for free at Marx.org, written by Lenin giving the Marxist standpoint on this issue if you want more information.
edit:
I wish to point out that the proletariat alone does not have to rule for socialism to be established, in Russia the proletariat and the peasantry ruled in alliance, as expressed by the hammer and the sickle.


