Other contributors have said "What are silas marner disabilities?" is the same question as "Who was Silas Marner?" If you believe that these are not asking the same thing and should be answered differently, click here
Though there is no main antagonist you could consider minor ones such as William Dane because of his betrayal of Silas Marner, Dunstan Cass because he stole Marner's money, or maybe even Godfrey Cass...