Oscar Alvarez is the son of Ramon Alvarez, the killed victim Riggs and Murtaugh were investigating the homicide case of, and Mrs. Alvarez.
He is portrayed by Peter Cortez.
Apparently, Ramon had stolen heroin from a drug dealer, Levon Tibibian, and his wife, Mrs. Alvarez, kept it well hidden, and Ramon was killed for it. Oscar, however, was kidnapped, in order to get the heroin back in exchange for Oscar to be released to Mrs. Alvarez. Riggs goes in to save Oscar, and Murtaugh soon after joined in and they killed the bad guys, including Tibibian, and rescued Oscar.