NPCs and Other Roles
You can go to GameFAQs to find the lists of SP Items in both Outbreak games. Reading the descriptions of the 40 unique SP Items can give you an idea of each character's personality. So can just hitting the "ad-lib" button a few times.
The Last Escape's Outbreak page and Resident Evil Fan are great places to find Outbreak images for icons.
This site shows the full list of costumes and NPCs for File #2, which includes the first game's NPCs. I'll list what's known about each one, while keeping it relatively spoiler-free:
Austin: a zookeeper at the Raccoon Zoo; he only shows up if you're playing on Hard or Very Hard. So committed to being manly that he's getting in trouble at work. The hunting rifle from "Wild Things" belonged to him.
Patric, Lloyd: a couple of surviving zookeepers. Both are apparently in awe of Austin's skills as a hunter; to wit, they note that if Austin's still alive, they're both gonna be fine.
Al, Axeman: all four costumes are the same guy, just in various different stages. Al is also the Axeman, who stalks the ruins of a hospital in the Raccoon Forest. (That isn't a spoiler. You know who he is the moment the Axeman shows up.) He apparently dies at the end of "Flashback."
Regan: Regan Morton, a survivor who appears in Al's cabin if you go for "Flashback's" Illusion Ending. She has a six-year-old daughter named Lucy.
Kurt: a former colleague of Alyssa's, he's dead long before the outbreak starts.
Marvin: the infamous Marvin Branagh of RE2/RE3 fame, Marvin is critically wounded over the course of "Desperate Times." He will go on to turn into a zombie over the course of RE2.
Rita: a pretty blonde patrolwoman with the RPD who survives "Desperate Times." She's kind of little, has a slight Southern accent and might've had a thing for Marvin.
Ben: Ben Bertolucci, crusading reporter with the Raccoon Press. He spends "Desperate Times" and RE2 locked inside a cell, and will get killed by William Birkin during the latter game.
Fred, Andy, Jean: various cops. Fred and Andy die during "Desperate Times," and Jean is found dead if you play "Underbelly" on Hard or Very Hard.
Tony: the RPD's K9 cop and a buddy of Kevin's. Dies during "Desperate Times."
Nathan, Samuel: convicts locked inside the cell next to Ben's. They escape the cell at some point between File #2 and RE2.
Linda: the savior of humanity, etc. etc.
Carter: Linda's colleague and a bona fide nerd. He was in Birkin's lab during "Below Freezing Point"; he's the guy who gives Yoko the Magnum on B5.
Arnold: A sniper and a commander in the Umbrella Biohazard Countermeasures Service, he killed 100 zombies during the outbreak.
Rodriguez: A helicopter pilot and an ally of Linda's.
Bob: Mark's co-worker and buddy. He commits suicide if you get him to the roof of J's Bar during "Outbreak"; on Very Hard, he turns into a zombie instead.
Will: the bartender at J's Bar. He's killed a few minutes into "Outbreak."
Raymond: the blond cop who saves your ass during "Outbreak," and gets killed in the process of so doing.
Arthur, Aaron, Dorian: random cops.
Eric, Elliot: the two cops who die at the barricade on the main street in "Outbreak."
Harry: after completely failing to distinguish himself during "Outbreak," Harry the cowardly cop will go on to drive Rita's escape van during "Desperate Times." That's right, folks: his cowardice fucks you over twice.
Monica: Yoko's former co-worker and a stone bitch, Monica is plotting to steal from Birkin's lab during "Below Freezing Point."
Frost: the Umbrella employee who Monica shoots dead in the first few seconds of "Below Freezing Point."
Hursh: despite one of the files identifying him as "Steve Jones," Hursh is the Indian doctor who dies in the first couple of minutes of "The Hive."
Ethan, Howard, Isaac: various doctors at the Raccoon Hospital.
Kathy, Elena: nurses at the Raccoon Hospital. They're the female nurse zombie templates.
Danny, Gill: a couple of firemen. Gill saves your ass at the end of "Hellfire," and I believe they're meant to be the two guys who're in the rescue helicopter at the end of "Decisions, Decisions."
Len: a fireman, Len and his buddy Charlie both die in an explosion at the start of "Hellfire."
Peter: George's colleague Peter Jenkins, the scientist who created the T-Virus antidote known as "Daylight."
Greg: Greg Mura, the creator of the Thanatos bioweapon, a crazy fucker, and the guy who operated on Yoko.
Karl, Dustin: random mercenaries with the UBCS.
Luke: renamed from "USS1". Luke is a soldier from the same squad as Hunk.
Nicolas, Sean, Philip, Don, Rodney: a bunch of random pedestrians. Rodney's a favorite of mine; he looks like Randall Graves and he's a Kevin-type.
Stickfigures: These are gratuitously weird "skins" for all eight main characters. I believe they've all got certain unwritten advantages over the main characters; for example, I know Mr. Gold is a Mark-type that gets 150% damage off all weapons, even weapons that you can't ordinarily crit or otherwise add damage multipliers to. (For example, Kevin can't potshot with George's ampoule shooter, and Jim's luck doesn't let you land a critical hit with it, but Mr. Gold will do 150% damage with it.)
Danny, Gill, Rodriguez, and Arnold are all verifiably survivors of the outbreak itself; Rita, Harry, Regan, Nathan, and Samuel all appear in scenarios but do not die over the course of them.
You can also use a Gameshark to unlock the "File #3" skins in File #2. These aren't too noteworthy. Off the top of my head, there's Amelia, who you'll see die in "Underbelly" if you get to the employee restroom fast enough; Ginger, the human version of the female zombie in the sleeveless top; a couple more Hunk-style Umbrella mercenaries; a black guy named Bone who's apparently a co-worker of David's; and... um... Hunk. Yeah.