Santiago was a major antagonist during Season 2 and Season 3 of Mr. Robot. He served as a FBI mole and a pawn to the Dark Army where he would provide important information to the Dark Army. He would try to sabotage the investigation in the Five-Nine Hack and cover for the Dark Army. Santiago would work alongside Irving to provide protection for Tyrell Wellick and try to sabotage Dominique DiPierro's effort for going after the Dark Army, Fsociety and Whiterose.
He was played by the actor Omar Metwally.
Santiago was once a loyal member of the FBI but having been blackmailed by the Dark Army to provide information for his family's protection, Santiago had no choice but to provide information to the Dark Army. As a mole for the FBI, Santiago was stressed and frustrated at having to give information to the Dark Army while trying to protect his own image. When events happen, Santiago would often times lose his temper and yell at anyone who happens to be around him.
While providing protection for Tyrell, Santiago has shown that he has no patience for slip up on the Dark Army's part as he, Santiago, has work to do for the FBI. When Dominique DiPierro (Dom for short) would have leads on the Dark Army, Santiago would often become more stressed as it interferes with his role in protecting and providing information.
In "Shutdown -r", Santiago was shown to violent when he was caught by Dom as he sucker punched her and kidnapped her alongside Darlene. He also explained to her that the reason he has to work for the Dark Army was because he had no choice or else his family would be killed. Before his death, Santiago pleaded with Irving to spare Dominique since he did not want to see her get killed by him and even acknowledge how she was a capable agent in the FBI.
With Dom, Santiago often got into disputes as to how to handle information related to the Dark Army and Fsociety. Because of Dominique's efforts, Santiago was stressed at his job and would make quick decisions that came off as irrational to Dominique. He expressed remorse at the thought of having her killed and tried to persuade Irving into making her a spy for the FBI than kill her which shows that he genuinely cares for her safety. When Dominique found out that Santiago worked for the Dark Army, she saw him as a traitor to the FBI until she realized personally that he was being blackmailed by the Dark Army to provide information for them.
Santiago was once a loyal member of the FBI and many people trusted him. After getting blackmailed by the Dark Army, Santiago was forced to give information from the FBI to the Dark Army much to his own frustration.
Santiago was enraged at Tyrell reckless decision to leave his hiding spot because Santiago had to kill a police officer to provide him protection. When he met up with Tyrell after the Stage 2 move by the Dark Army and Fsociety, Santiago was cold to Tyrell and warned him to not go against the Dark Army.
As a person he had to report to, Santiago looked to Irving for how to deal with hard situations. Santiago would often complain to Irving about how his job at the FBI and his role in providing information to the Dark Army was stressful. Santiago treated Irving as his superior when it came to working for Dark Army and would try to negotiate with him to spare Dominique. However, to Irving, he saw Santiago as a jerk and someone who was incompetent to allow Dominique to catch him and felt nothing when he had to dispose of Santiago so that Dominique could replace him.
With the Dark Army, Santiago did not like them and was often stressed and ashamed that he had to work for them against his will. Santiago did not like what he had to do for the Dark Army but was loyal to them only because his family's lives were endangered. With his involvement with the Dark Army, he was very stressed by them.
With Darlene, Santiago saw her as an important piece to getting information from Fsociety. However, he would treat he harshly when he forcefully handcuff her and capture her so that she would be killed by the Dark Army.
Santiago deeply cared for and loved his mother. He wanted her to stay safe and was willing to betray the FBI and work for the Dark Army to protect her from the Dark Army. He admits to Dominique that he had to do what he had to do because his mother's life was endangered by the Dark Army if he did not follow their orders.
In the past, Santiago earned a high position in the FBI. At some point, the Dark Army approached him and threatened to kill his family if he did not constantly provide information to the Dark Army. Santiago reluctantly joined the Dark Army and began to give information to them so that his family could be protected.
The FBI was onto to the activities of Fsociety. With the United States undergoing negative effects from the Five-Nine Hack, Santiago played a role in providing important details to the Dark Army. During the season, Santiago provided information to the Dark Army to have the members find and kill Cisco before Dominique would get to him. Towards the end of the season, the FBI was able catch Darlene Alderson so that they could use her as a pawn to spy on Elliot Alderson. Santiago and the FBI did not know the whereabouts of the other Fsociety members, Trenton and Mobley.
Santiago provided protection for Tyrell Wellick, a key figure in the Five-Nine Hack, by providing a hiding place for him out near the forest. He also worked with Irving to continue to give more information to the Dark Army. When Tyrell escaped from the house he was at and was caught by a police officer, Santiago killed the police officer and brought Tyrell back to house. He angrily chastised Tyrell his for reckless decision and complained to Irving how stressful the job is.
When Stage 2 of the Fsociety and Dark Army plan went through and 71 buildings were destroyed causing thousands of death, Tyrell escaped from his hiding place and the law enforcement caught him. Santiago met with Tyrell in private to tell him that his wife, Joanna is dead and that his son is in the system. Santiago threatened Tyrell with doing something bad to his own son, if he did not comply with the Dark Army's instructions. After the meeting, Santiago was visibly shocked at the destruction that he played a role in and reminded his mother that things will work out and to be safe.
Santiago later appeared with law enforcement officials where they discovered the dead bodies of Trenton and Mobley. He would use this alongside the Dark Army to frame Trenton and Mobley as the masterminds behind the terrorist attacks.
When Darlene was caught by Dom attempting to steal her FBI card and was sent to the agency, Santiago was surprised to here that the Five-Nine Hack could be undone. After hearing this and calling Irving for some assistance, Santiago forced Darlene into a car. When Dom saw what he was doing, he sucker punched her and captured them. Santiago drove them to the hiding spot where Tyrell was at. He told Irving that he had to capture Dom since she saw what he was doing. Irving led them Dominique outside the barn house to a log pile. Irving took up an ax and was ready to cut down Dominique. Santiago tried to negotiate with Irving to spare Dominique as she is a skillful agent at the FBI. To Santiago's shock, Irving attacked him with the ax and told Dominique that she will now be Santiago's replacement. Irving continued to chop him up with the ax. Much to Dominique's shock, she was now Santiago's replacement as the FBI mole.