|Relationships||Hiroshi Hatake, co-conspirator|
Constance Sutton, ex-lover (deceased)
Julia Walker, Ex-lover
Major Sergio Balleseros claimed to be an Army officer assigned to USAMRIID and a systems engineer. He hates rats. He said his experience included a tour in Iraq, looking for WMDs, and time in South America "harassing the cartels." He said he had spent time at Sandia Laboratories.
After discovering that Dr. Tracey had attempted to break out of ABS, Sergio finds Dr. Henrik DeKlerk hiding in a stairwell and tackles him. He also catches Dr. Graff trying to leave the base and ends up murdering him.
When Doreen discovers that the virus was man-made, and identifies the DNA sequence involved, he attacks her with a syringe, injecting air into her carotid artery. She dies, and he stages the scene as an accident, dumping infected rats on her body.
Balleseros is captured by Constance Sutton's security team. Constance slaps him for murdering Dr. Doreen Bryce and then kisses him. She finally sends him to solitary confinement.
He engineers an escape from Arctic BioSystems, but as he is trying to steal Anana's snowmobile, she confronts him and delays his escape. When Constance Sutton's security team discovers Balleseros and Anana, he gives her the gun and the snowmobile and tells her to go, because security would kill her but not him.
Balleseros breaks out of confinement with Lieutenant Klein then kills Klein both for his cold weather clothing and because he was a threat. He and Daniel Aerov head toward the Inuit village and are intercepted by Anana. The three work together to prevent the murder of the residents of the village.
A well-dressed Sergio talks to Peter Farragut on a cellphone from within the Illaria corporation telling him the mission stays the same.
Sergio and Julia Walker are having sex. Sergio gets a message on his phone saying the Illaria corporation board meeting was rescheduled to an hour ago.
Sergio and Julia Walker arrive on the island of St. Germain to retrieve Brother Michael in an attempt to prevent the newest NARVIK strand from being unleashed upon the world in 4 days. Despite Julia saying that they shouldn't have any problems, Sergio isn't too certain and cocks his gun. Upon arriving at the Abbey, Sergio knocks on the door and meets Sister Anne and Peter. Upon introductions, he tells Peter not to call him "Sergio".
Sergio and Julia Walker discuss Amy's request to become immortal, stating the world doesn't need a, "forever Amy." Sergio is tasked with shadowing Sister Amy around the Abbey, making sure she keeps up her end of the bargain. Sergio reveals his harsh nature when Sister Amy tries to play games with him, trying to slice him open with a razor blade and then lapping up his blood with her tongue like a vampire. Upon arriving at the very top of the observatory Sergio is ambushed by Landry and the two fumble around, however Sergio is able to throw Landry off of him, sending him hurtling down the stairwell, however not at the cost of losing his balance. He is hanging on for dear life upon which Sister Amy kicks him in the head, sending him spiraling down where he hits his head on the side of the stairs.
Julia Walker and Sarah Jordan happen upon Sergio's lifeless body, confirming his death. Julia states how he was a trained assassin and is very upset by his passing.
- Balleseros wears a garment in the Army Combat Uniform pattern which is not an actual U.S. Army uniform, using the sleeves and collar in an unusual way for a regular Army soldier.
- In "Aniqatiga", Balleseros wears the Army green instead of the current Army blue uniform.
|Episodes|| "San Jose" • "Reunion" • "Scion" • "Densho" • "Oubliette" • "M. Domestica" • "Cross Pollination" •|
"Vade in Pace" • "Ectogenesis" • "Mother" • "Plan B" • "The Ascendant" • "O Brave New World"
|Primary Characters||Alan Farragut • Julia Walker • Peter Farragut • Sarah Jordan • Kyle Sommer • Sergio Balleseros|
|Secondary Characters|| Brother Michael • Sister Amy • Sister Anne • Sister Agnes • Landry • Caleb •|
Lt. Commander Winger • Hiroshi Hatake • Daniel Aerov • Leila Weisner
|Season 1 • Season 2|
|Episodes|| "Pilot" • "Vector" • "274" • "Single Strand" • "The White Room" • "Aniqatiga" • "Survivor Zero" •|
"Bloodline" • "Level X" • "Fushigi" • "Black Rain" • "The Reaping" • "Dans L'ombre"
|Primary Characters||Alan Farragut • Julia Walker • Sarah Jordan • Hiroshi Hatake • Daniel Aerov • Sergio Balleseros|
|Secondary Characters||Peter Farragut • Doreen Boyle • Jane Walker • Anana • Toluk • Constance Sutton • Spencer Chissik • Philippe Duchamp • Sulemani • Victor Adrian • Bryce • Rae Van Eigem • Klein • Thea • Dimitri Marin • Haven • Blake • Tracey|
|Season 1 • Season 2|