Alvin Brock is a character who makes a one-time appearance in the Season 3 episode titled "Wildfire".
Alvin Brock is one of the drug pushers working with Carlos, Noble Flowers and Moose to bring in drugs using Big Cece's oil refinery as a cover. When Little Cece was convinced by Dominic to refuse to deliver a shipment and thus expose his operation, he and Carlos went after the Cece family. They caught up with them in a hotel. Alvin demanded that Big Cece hand over his package of drugs but Big Cece and Dominic overpowered him and Carlos in a coordinated attack which they had developed during a bar fight when they were servicemen in Korea. Alvin and Carlos were knocked out and it is likely that Dominic and Big Cece would have tied them up for the authorities to pick up later.
Among the gang of pushers, Alvin appears to be the "brains" and leader. Noble Flowers would say things like "Alvin wouldn't like that". It was Alvin who worked out the most likely place Dominic and Big Cece would hide out.