"Little" Stevie Dwyer was a stick-up merchant and one-time friend of Sonny Corleone.
Along with Corleone, Bobby Corcoran and several others, Dwyer held up several trucks and made small-time robberies. When the gang offered their cut to Luca Brasi, he accepted, but would not do business with Dwyer due to his Irish heritage and stupidity (during a meeting with Brasi and his gang, he exited a truck inadvertently pointing a machine gun in Brasi's direction), leading him to be shunned.
Personality and traits
Even whilst a member of Sonny's gang, Stevie was not particularly well-liked by other members of the gang due to his unpleasant nature, and it was this that got him shunned, particularly after he insulted Bobby "Cork" Corcoran's sexuality. Many felt his hot head and his knack for rubbing people the wrong way would lead him to trouble. This prediction especially came true when Corcoran violently assaulted Stevie for the aforementioned insult.