Though Delta is an Active stationed out of the Los Angeles dollhouse, I don't expect all Dollhouse characters to remember him or muns to take him as part of personal canon (he is a fandom OC, after all). If you'd like to have your character remember him, this is all of the relevant information; if you'd rather not, no worries!
A few notes:
Delta does not have perfect control over his imprints. Most of the time, the Benjamin imprint is in command; Benjamin is not a fighter, and he isn't programmed with a whole lot of useful skills, but he can control the other imprints.
There is no meta-Delta personality, as such, because of the suddenness of the composite event. He is no Alpha or Echo; there were no signs of growing awareness, before the accident. He will be unable to deal with imprints long-term without severe medical problems.
Noah Fielding was married at nineteen, and had a young daughter before he was twenty-one. Utterly in love with his wife, enamored with his daughter, and unconcerned, for a time, about his own life, the possible progress of his career, the direct application of the natural intelligence that had landed him in gifted programs all throughout high school.
Supporting a family was more difficult than he'd thought. College took nearly a decade to finish entirely, with the number of times he dropped out. Graduate school, out of the question. Money was tight, ends had to be met, and Noah took a job as a lab tech in a research company, a rival of Rossum.
When his wife and daughter were killed in a car crash, he went mad with grief. After unsuccessfully attempting to sell his company's secrets to Rossum, and nearly getting arrested, he was eventually offered the life of an Active. When he signed the paperwork, he didn't expect to ever get his life back.
Delta joined the Los Angeles dollhouse a little over six months before Alpha's composite event, and a little over nine months before the beginning of the television show timeline. Being an older doll, and thus not very high in demand in the youth-oriented Los Angeles market, Delta was a relatively less-used Active, though crucial in engagements where something different from the norm was requested.
As a doll, he was well within normal behavioral and neural parameters. He had a tendency to watch others, perhaps a hint more than he should have, but there was very little to distinguish him from the crowd.
(in order of imprinting:)
1. Adam (priest)
2. Leo McCoy (doctor)
3. Owen (fantasy husband/massage therapist)
4. Thomas (therapist)
5. Aiden (sailor)
6. Peter Alexandrov (Russian professor)
7. Edward (Victorian gentleman)
8. William (Victorian stage magician)
9. Christopher (Victorian thief)
10. Gibson/Snapper (weapons expert/bodyguard)
11. Robert (serial killer victim)
12. Elijah (babysitter/childcare expert)
13. Jace (serial killer)
14. Jack (businessman/spy)
14A. Ninja Assassin, code-phrase activated
15. Zachary (chef)
16. Campbell (homeless veteran)
17. Elias (bad-boy)
18. Seth (grieving widower)
19. Benjamin (BDSM dominant)
20. Nolan (physicist)
THE NINJA ASSASSIN
The code phrase to activate the 14th personality's sub-imprint is, following the form of November's: There are three birds in the yard. The third bird is red.
Deactivation is: There are three birds in the yard. The third bird is yellow.
Delta is not aware of these code-phrases, and it is impossible for him to learn them. The activation works regardless of which imprint is currently active.
THE FIRST DEVIATION
On Benjamin's engagement, he was intended to be a BDSM dominant for man with too much time and money on his hands. Instead of fulfilling the mission parameters, he talked the client down from his wants, brought the client to tears, allowed him to come to epiphany about himself and his needs, and then had some sweet, intimate sex that morning. There was no BDSM involved.
He was nearly sent to the Attic for going so far off-parameter, but it was eventually blamed on the imprint, not on the active, and he was sent out on the long-term engagement anyway.
THE LONG-TERM ENGAGEMENT
Nolan, Delta's last imprint, was hired by a government-contracted company to do experiments in theoretical physics. During one such experiment, safety parameters were overloaded, and Delta experienced a blast of energy that not only altered his brain irreparably but also allowed all previous imprints to surface (though it appeared to wipe Nolan out of Delta's brain permanently).
THE COMPOSITE EVENT
Where this may have driven any other Active insane, the presence of Benjamin, an already exceptional personality, was able to give the multiple imprints some kind of structure and control. The neural stress may eventually kill him, but, for now, he has been able to retain his sanity.
Though Delta escaped from his handler, intending the preservation of his twenty personalities as a moral choice over allowing them to be eliminated, he was unaware of the tracker implanted in his neck, and was quickly captured, deemed 'broken', and sent to the Attic, just on the heels of Laurence Dominic.
Delta was a doll for only a year before being consigned to the Attic.