Oscar is a prisoner survivor who joins Rick's group in AMC's The Walking Dead. He makes his debut appearance in the Season 3 premiere alongside Axel, Tomas, Andrew, and Big Tiny. Unlike some of the other prisoners (namely Tomas and Andrew), Oscar is brave, honourable and much nicer, along with Axel and Big Tiny. At first, Rick and his group were distrusting of Oscar and Axel, but when they soon prove their loyalty by killing the hostile Andrew and clearing out the remaining walkers that Andrew had brought into the Prison as part of his attack, Oscar and Axel are finally accepted into the group. Both Oscar and Axel prove to be rather vital members to the group: Oscar for his strength and Axel for his mechanic skills. He dies in the Woodbury assault while trying to save Glenn and Maggie in the mid-season finale of Season 3. Oscar served as a supporting protagonist during the first half of Season 3.
3x01: "Seed" (No Lines)
3x04: "Killer Within"
3x05: "Say the Word"
3x07: "When the Dead Come Knocking"
3x08: "Made to Suffer"
Oscar is the fourth prisoner survivor to die (and the last prisoner to die in the first half of Season 3).
Oscar is the only prisoner out of all five to enter (and die in) Woodbury and the only prisoner to die outside of the Prison.
Though they are best friends and look out for each other, Oscar and Axel have several differences:
While Oscar is African-American, Axel is Caucasian-American.
While Oscar is tall, brawny and physically strong, Axel is short, thin and physically weak.
While Oscar is brave, calm, quiet and serious, Axel is timid, excited, talkative and funny.
While Oscar is more competent in killing walkers and has killed a few (bad) people, Axel is somewhat capable in killing walkers and has never killed anyone.
While Oscar is not afraid of dying and refused to plead for his life when Rick pointed a gun at him, Axel is afraid of dying and pleaded for his life when Rick pointed a gun at him.
While Oscar knows how to use guns and is not afraid to use them, Axel doesn't know how to use guns and is afraid of them.
While Oscar died outside the Prison, Axel died inside the Prison (both of them were killed by the Woodbury Army led by The Governor).
Both have no Comic Book counterparts, therefore they are original characters to the TV show.
Both are bald African-Americans.
Both are silent at most times.
Both serve as a source of muscle for Rick's group.
Both are kind, brave, selfless, honourable and competent against walkers.
Both their back-stories are hardly known.
Both started off as quite clumsy and uninitiated, but grew to be better and more competent assets to the group.
Both have fought against an antagonistic member of their own group (Merle for T-Dog, Andrew for Oscar).
Both went on a rescue mission for someone that they are not very close with (Merle for T-Dog, Glenn and Maggie for Oscar).
Both died in the first half of Season 3, and both died whilst helping a friend get to safety (Carol for T-Dog, Glenn for Oscar).
Also, while they are essentially different, Oscar can be considered to be the TV counterpart of Dexter, another prisoner survivor and an antagonist in the Comic Series. The reasons are that:
Both men are bald, tall and physically tough African-Americans.
Both men have killed at least two people (Dexter killed his wife and her lover before the apocalypse, and Oscar killed Andrew and at least one unnamed Woodbury soldier after the apocalypse), but while Dexter's kills were unjustified, Oscar's kills were.
Both men had an antagonistic, distrustful relationship with psychopathic prisoner survivor, Thomas/Tomas.
Both men have been wrongfully accused of crimes that one of their "fellow" prisoners committed, but were soon proven innocent (In the Comic Series, Thomas Richards killed Hershel's twin daughters, Rachel and Susie, and Dexter was wrongfully accused of it since he was thought to be the only prisoner inside for homicide, and in the TV Series, Andrew lured a massive number of walkers into the Prison and tried to kill all of Rick's group and take the Prison back, which resulted in the deaths of T-Dog and Lori Grimes, and Oscar, along with Axel, were wrongfully accused of the attack since they were thought to be the only prisoners left alive and were thought to be as dangerous as Andrew and Tomas).
Both men wield shotguns, and both men have aimed guns at Rick Grimes, although while Dexter was antagonistic towards Rick until the end of his life, Oscar changed his mind about killing Rick and killed hostile prisoner Andrew to save Rick, thus earning Rick's trust and establishing a place in the group.