Most think that the people, who founded the party, didn't believe in Socialism but only wanted to get party members from the working class. That's why the party origianally was called DAP (Deutsche Arbeiter Partei)
[German Workers' Party].
When that got the 'NSDAP' in 1920, Hitler [and Eckart, Esser, Heß, Röhm, Feder] added the 'NS' to the party's name without informing the party's leaders. (The name was already used - though a bit differently - by an Austrian party, DNSAP.)