Corporal Rivera was a Marine who served on Makin in the misson "Semper Fi". He was seen when Miller did not follow Sullivan and Roebuck but instead went on the platform with Denny, Snider, and Slayback at the beginning. Near the end of the platform the player can see a Japanese soldier and a Marine fighting, which is Rivera. If the player takes the right with Sullivan and Roebuck, Rivera will die. But taking the left gives the player a chance to kill the Japanese soldier. Rivera will try to find cover but can be killed while doing this. If he lives then he will be with the others who are fighting the MG nest. After that and the Banzai attack, he will die with Rooker and Lozano at the second gunfight.
Strangely, if Rivera and Lozano live through the MG nest then Denny will die for no reason like Ryan would. Rivera held a Thompson. Also if Lozano and/or Rivera live Rooker will die at the second gunfight by being shot instead of the ambush where he is stabbed.