Melkor was the equal in power of Manwe, the chief of the Valar. So, basically, when he went bad, he was about as bad as it was possible to get. Sauron was less bad, to quote Tolkien, 'only because for many a year he served another'. Melkor's name meant 'He who arises in power'. He was renamed 'Morgoth', meaning 'the black enemy' by Feanor after the theft of the Silmarils

Incidentally.....'sour' IS the correct pronunciation for the first part of Sauron's name. The name meant 'The Abhorred'

OK...thats enough from me...I think I have overdone the sadly encyclopedic knowledge of Tolkien, and must now return to the real world