On the island...
The "blonde guy" is a nickname given to one of the Oceanic Flight 815 tail section survivors.
During their first night on the Island, three of the tail section survivors were kidnapped by the Others. The "blond guy" was among these three survivors. ("The Other 48 Days") Although he was not specifically identified in any scene, he was later mentioned by Nathan:
From "The Other 48 Days" transcript:
Nathan: Look, three of the people are missing — the blond guy, the curly-haired guy, and the German who was helping us with the injured.