I've found that while coming up with an elaborate backstory for fixers is fun, it also tends to be a lot of work for sometimes(often) very little use. I like having the main outline for their history because that can explain personality quirks, friends and enemies, and what type of contacts and jobs they tend to have for the Runners, but it's a very rare thing that the players will want to know or even actively look into the detailed life story of their fixer. Having said that, I'll post some brief examples of ones I've used or am actively using in my game.
Spencer Craig, AKA "Psycho Skydive"
Based out of Atlanta, Psycho Skydive got his street name in the combat biking scene of the 2050s-2060s, where as the star player for the Lightning Riders, he got knocked off his bike mid-air and somehow managed to dive-bomb one of the opposing players off their bike in the final moments of the game, a move that is still talked about decades later. And while a number of injuries and replacement parts from his career have left him unable to play the sport anymore, he's still involved as the hands-on owner of his team, training the Riders and scouting for new talent.
With feathered platinum-blonde hair, a mile-wide smile, and a constant smell of cologne and motor fuel, Psycho Skydive is an adrenaline junkie and motorsport enthusiast for life, heavily involved in the Atlanta racing, combat biking, and urban brawl circuit. He turned to using his connections with various teams, players, and managers/owners to part-time fixing(and being the occasional Johnson) when he saw that a LOT of nuyen was trading hands behind the scenes, and some of it should be used to help out up-and-coming talent instead of lining the pockets of people who barely had any involvement or interest in his beloved sports. With a wild personality and slightly crazy, "Hell yeah balls-to-the-wall" attitude, Psycho Skydive's jobs tend to revolve around motor sports and fast-paced pursuits. However, he has a good heart and good intentions, and will never actively try to screw over a team or hide info from them, and if they do well for him they'll have a solid friend and Fixer in the CAS shadows(and maybe he'll even get you season tickets to the Lightning Riders' games).
The Baroness
With a low southern drawl, expensive tastes, and even good looks(for a troll), the Baroness seems the very essence of CAS charm, hospitality, and refinement. However, very observant Runners or those who do a fair bit of digging may notice that her accent slips just slightly every now and then, or that it almost seems like she's going out of her way to make sure everyone knows how fancy she is. The reason for this is simple; being a troll in the CAS, she grew up poor and without many of the opportunities that the prettier(or less savage-looking) metatypes took for granted. She's done a lot of things she'd rather not speak of to get where she is, and has made a very concerted effort to forget about her checkered past, even if she can never completely erase it entirely. However, she does a job of hiding who she is and where she came from; as far as anyone who matters is concerned, The Baroness will do.
If Runners work for the Baroness, they'll be meeting her in fancy restaurants and clubs around the Atlanta Metroplex, and her jobs will take the team all over the CAS and southern half of the continent, though rarely in Atlanta itself("You should never work from home, Dahhhling, it confuses business and pleasure."). The other thing is her ruthless climb to the higher echelons of society carries over to her taste in jobs and relationships with Runners. She prefers professionalism, but if that means a heavy body count or collateral damage, then so be it. Whatever it takes to get the job done is acceptable. Failure is not, and just as she'll treat her main teams VERY well with nuyen, favours, contacts, and other opportunities, she won't hesitate to burn anyone and everyone to the ground if she finds out they've been double-dealing or otherwise failing her high standards.
Timothy Dean Hollins, AKA "Titan"
If you you were in the shadows of the UCAS, PCC, or Sioux Nation in the 2060s, you might have run across a Shadowrunner called Titan, known for being a juggernaut with a troll-sized combat axe. If you looked up the name Timothy Hollins in the mid 2050s, you might find a professional bodybuilder that went from up-and-coming star to disgraced and disqualified competitor due to a scandal involving experimental muscle-fibre gene treatments. The truth is both are one and the same, and after his name becoming synonymous with cheating on a genetic level, Titan fell off the grid and into the shadows. After a decade of running, he and his fellow runner turned best friend Sal finally hit that elusive big score, earning enough to get some rejuvenation treatment and sink the rest into a little Runner bar in the Redmond Barrens.
Now, after Sal's recent death, Titan finds himself restless with retirement, and while he doesn't want to go back to getting shot at(or stabbed, or fireballed, or that one time with the Pixie from Hell), helping get jobs for new Runners, and maybe teaching them a few things to help them survive in the shadows scratches that itch just enough to keep him busy. He doesn't get the highest-paying jobs in the world, but the work is steady and mostly honest. And, if a Runner needs some help with physical conditioning or building muscle, Titan has a personal gym and years of experience to will whip any would-be musclehead into fighting shape.