Daniel Francisco "Danny" Avila was a human living pre and post-Judgment Day. He, and was an accomplished member of the Human Resistance. He was the one-time-lover of Michaela Herrera and father of her son; Mark Herrera, both of whom joined the Resistance.
Danny was born to Hugo and Teresa Avila, the youngest son of three. Danny was raised in the company of his family on their family farming estate, and grew up to care about them very much. Like his brothers, Danny did not pursue a farming career; and instead found his stride in computers. Daniel became an expert on computer technology and programming.
Daniel, after university, secured employed by the United States Air Force as one of their civilian employees. He became the lead programmer on the team based at Edwards Air Force Base; working on the Skynet Project (specifically dealing with the creation and development of the early Terminators). Daniel was very passionate in his job, having a considerable reputation (even with the head of operations - Lieutenant General Robert Brewster) as being the best member of the team, and had the highest of hopes for his work.
However, Daniel had, unknowingly, become gradually irradiated, from a distance, by the Continuum Transporter based on Edwards AFB. The effects eventually gave Daniel the ability to send his consciousness via. a two-way psychic link to his future self. Daniel was horrified to see the world as it was after Judgment Day; and eventually Resistance members convinced Daniel's younger self of the truth.
Knowing nothing could be done to stop Judgment Day; Danny worked to secure resources and knowledge for future use, as well as implementing a clever plan to upload a virus into Skynet, the moment Judgment Day is initiated, designed to erase all information pertaining to certain decommissioned military facilities, minor military storage facilities & armories, potentially useful cave systems etc.
It was during this time that Daniel finally consummated the feelings of attraction he held for Michaela Herrera (or otherwise known to him as Linda Avila - his widowed sister-in-law and a deputy sheriff who served alongside her husband and one of Daniel's brothers; Alex, who was shot and killed in the line of duty several years before). When Daniel awoke from nightmares, Linda was there to comfort him, and Daniel surprised her by kissing her. Instead of the rejection he expected, Linda, sharing his feelings, proceeded to have sex with him; and unknowingly conceive and become pregnant with Daniel's baby.
Skynet eventually became aware of Daniel's activities (though not in enough detail to realize his plans) and deemed him a potential threat. To this end, Skynet expertly forged e-mails to General Brewster hinting Daniel was secretly a foreign agent for the Chinese, planning to steal Terminator & Skynet technology and sell it to them, and at the same time arranged to have Scowl; the first prototype Terminator unit, sent out on a field test, only for it to murder its two CRS handlers and attack the Avila estate, killing Teresa and all of the farm hands, and thus leave Daniel as the only suspect. With assistance from his future allies, Daniel convinced Linda of his innocence and worked together to evade the authorities, and ultimately lure Scowl into an ambush and destroy it with C4 explosives.
With Judgment Day minutes away, Daniel and Linda momentarily separate so Linda can try to reach her extended family in Texas, while Daniel sorts out the escape route from Los Angeles. While alone, Daniel suffered a stroke; caused by the intense physical stresses of using his ability for so long, which, while leaving his body unharmed, did significant damage to his brain and caused him to loose all of his memories. In a daze, Daniel wandered off and was rescued by survivors, who he traveled with from then on, completely unaware of his identity.
Linda, meanwhile, after finding Daniel missing, was forced, in the chaos that followed, to go on without him. In the meantime, she re-adopted her formal name of "Michaela "Mike" Herrera" to gain a new identity, and continued her pregnancy and eventually gave birth to her and Daniel's son - Mark; named after Mike's favorite uncle who, along with the rest of her family, are believed to have been amongst those who perished during Judgment Day.
Time with the Resistance
Daniel eventually joined John Connor and Kate Brewster's resistance movement, and soon ascended to the Senior Command Staff as John's programming adviser. While taking in bands of survivors into the Resistance, among those was Mike and a 6-year-old Mark. Mike quickly realized Daniel no longer remembered her, or the feelings he had had for her, and so, for the sake of their son, decided to pretend to not know him, but did help in re-discovering jumbled parts of Daniel's identity.
Daniel would serve with the Resistance for years, becoming nothing more than a comrade-in-arms to Mike. Meanwhile, Mike did indeed let Mark learn the truth of his heritage when he turned 18 years of age (feeling Mark was too young at the time to learn of, or even understand, the reasons why his father could not be there for them; and so Mike felt it would do more harm than good). Mark accepted it and the two kept it a secret.
Eventually, Daniel re-discovered his ability and Connor and the rest of the Senior Command Staff used it as an opportunity to alter several events in the past to the Resistances' advantage (specifically by utilizing the plan with the modified virus); with the advisers helping Daniel's younger self along the way during the events leading up to Judgment Day.
After a time, however, Daniel's ability took its physical toll on him to the point it caused him to have a stroke - leaving him partially-crippled. Also, a unique form of radiation Daniel's ability emitted very broadly eventually got Skynet's attention; and so led to the fall of Hornet Compound, the compound habitat the group was staying in and using as the location for the time-travel project. The base was evacuated successfully, however, and at Daniel's request the operation continued until it was completed successfully to ensure the timeline's stability.
After a time, Daniel, despite his body being broken, repaired his mind and eventually regained his memories - including that of Mike. Daniel was moved to tears of happiness when he learned he was Mark's father, and looked forward to continuing his relationship with Mike, getting to know his son, as well as continuing his Resistance duties (alongside physical therapy for his injuries).
However, it was not to be, Daniel had an epiphany - he could his ability to travel even further back in time and implement subtle programming changes to the Terminators that, while also undetectable by Skynet, would eventually bestow upon them a sense of independent sentience and could save millions of lives in the future. Despite the desperate protests of Mike, Connor reluctantly allowed Daniel to proceed, knowing the strain on his weakened body would kill him. No sooner had he finished, Daniel's body succumbed to the strain and had another stroke - killing future Daniel instantly and erasing past Daniel's memories (thus truly finishing the timeline). The entire staff was devastated at Daniel's death, but none more so than Mike.
Daniels's ashes were interred by his lover and son in the ruins of the Avila property - with the bag containing his ashes buried in the ground with a metal plaque on top inscribed the words "Daniel Fransisco Avila. Greater Than The Sum Of His Parts".
While he does not possess his father's family name, Mark lives on as the last of the Avila and Herrera families. Daniel, meanwhile, is more widely known for having secured the massive amount of resources, vehicles and other resources from control by Skynet; which are even now being re-discovered and utilized in the War Against The Machines.