Characters
The info is straight from Wikipedia (The best character info I've found!) Will be updated as more info pours in:
Shin-Ra Electric Power Company
President Shinra

The man with the most power in the Shin-Ra Company. Founder and President of the Shin-Ra Electric Power Company, his ways of controlling the world are by controlling the media and claiming that he is doing all he can to help the people. He is the also the father of Rufus Shinra.
Rufus Shinra

Son of President Shinra and Vice President of Shin-Ra, Rufus had different views on how to control people. He did not not have much influence over Shin-Ra at this time due to an extended business trip.
Reeve Tuesti

Shin-Ra's minister for housing and urban development. He was Midgar's architect, and designed the Mako reactors.
Hojo

Shin-Ra's head of science, and Professor Gast's successor. Despite his brilliance, he's a bit of a maverick, and a bit of a hack. Takes a childlike delight in developing all kinds of genetic monsters, as well as experimenting on humans.
Heidegger

Shin-Ra's chief of military. In episode 9 - A Step Further into Uncertainty, he briefly takes over from Veld command of the Turks and proceeds to run them into the ground until Veld manages to regain his position by bargaining with President Shinra.
Scarlet

Appears in episode 21 - The Preparation to Dive into the Finale, apparently in the same position as she held in Final Fantasy VII.
Professor Rayleigh
Female Shin-ra Inc. scientist. Shows up in episode 5 - The Dream of a Nameless Soldier, in which the player must guard her and the information she caries, along with two other SOLDIERs and SOLDIER-grunt Cloud Strife.
Turks
Verudo

The newly introduced character is in charge of the Turks, organising their missions etc. He is a man who is very particular when it comes to mission success and very unforgiving when it comes to failure. He is feared by all of his colleagues. When Heidegger usurps his place as head of the Department of Administrative Research in episode 9 - A Step Further into Uncertainty, he blackmails President Shinra into giving him back his job. Formerly a resident of Kalm Town, he had a daughter and wife that perished when the town was razed due to (his) misheard commands during the Wutai war, as discovered in episode 13 - A Scar that Disrupts the Peace.
Tseng

Despite being quite young, he is extremely loyal and respectable of his superiors. He admires Verudo's sense of professionalism and plans to emulate it one day.
Reno

A young turk who enjoyed doing things his own way. Depsite the fun, outgoing nature, when it comes to missions, he strives for success whilst still doing it in a very cool manner.
Rude

A large build man who has suffered from hair loss. He is often very quiet and does not socialize much, but is very caring to his colleagues. Despite his quiet and shy attitude, he is a very fierce and powerful fighter and often wears sunglasses.
Unknown Male A

One of the playable males. An ex-gang leader from Junon, he enjoyed fighting other gangs and stealing bikes, riding around causing havoc. Highly skilled in hand-to-hand combat as well as the ability to ride motorbikes and fixing them. He was rather unfamiliar with failure and with his ever growing confidence, decided to raid to Shin-Ra to steal some bikes, but was arrested by Reno. Realizing his skills could be used to achieve fame and fortune, he decided to offer his services to the Turks. He enjoys using the weapon "Electro Rod", a metallic rod that emits electrical shocks of sorts.
Unknown Female A

Her father being a teacher at the Shin-Ra Militia Academy, she decided to enrol to the Academy. Graduating with outstanding results, her forte was marksmenship. Her excellent handling of firearms impressed the leader of the Turks, Tseng and he decided to recruit her to the force, with great confidence in her. She is a very serious female who rarely jokes around, and is due to this, is often very strict. Her weaponry is generally guns. Her younger sister is Elena.
Unknown Male B

A former bodyguard of Don Corneo, his specialty is his rapid fire of guns with outstanding accuracy, much like Female A. Spending most of his time in the slums, he became fed up with the politics that had over-run the underworld society and he was offered a role in the Turks. He took up the role, knowing that it would put his skills to the test. His ruthless and "undergound" style of achieving his missions often resulted in him failing. His weaponry is mainly firearms.
Unknown Female B

A female hunter who often did things in a flashy manner. Always dressed as a person who came from a wealthy family, she had familiarized herself with the art of hunting ever since she was a mere child, specifically handling a shotgun. With a personality that liked to show off, she always wanted to better herself by accepting almost any job and when she was offered a place in the Turks, she immediately accepted. Her weaponery is a range of shotguns.
Unknown Male C

He is an ex-detective from Costa del Sol, where he solved some rather complicated cases. A passionate, hot blooded and courageous man, he puts his all into everything he does ? a trait that carries through to his personal as well as professional life. His tendency to rely on his emotions eventually got the better of him. He got himself into trouble, presumably in the course of his work and, finding no way out, took the job offered to him by the Turks who had been recruiting him for some time. He uses his powerful fists as a weapon to punch enemies. He also appears in Last Order: Final Fantasy VII and is credited as Turk (Martial Arts).
Unknown Female C

A mercenary recruited into the Turks when Veld decides that they are lacking the required manpower to deal with AVALANCHE. As a mercenary, she has seen a lot of battle, and is certainly used to taking orders, so her adjustment into the Turks is easier than it has been for some. A thoroughly businesslike woman on a mission, she gets her work done with a minimum of fuss. She is level headed, alert and perceptive, and is able to assess a situation and take the most prudent course of action. She is a skilled martial artist who uses a style which involves a lot of jumping and kicking style. She also appears in Last Order: Final Fantasy VII but has no speaking part.
Unknown Male D

Fencer who was born in Gongaga and has a soft spot for beauty. He does not tend to stay long in any one place. His hometown fears him for his power; It's said that he killed an entire group to rescue a friend of his and as a result was imprisoned. Under the condition he would join the Turks, however, he was bailed. He joins the player in episode 18, A Cry that Rings Throughout the World.
Unknown Female D

Girl who uses a throwing star and whose birthplace is not known. She has a mothering side and tends to look after her colleagues. She was recruited with intent for her to become a Turk while still in an orphanage. She was brought up under their harsh training techniques from a very young age; in the history of the Turks, she is the youngest member to join. She joins the player in episode 18, A Cry that Rings Throughout the World.
SOLDIERS
Sephiroth

A successful 1st-Class SOLDIER who came from Nibelhiem, Sephiroth showed fighting capabilities far superior than that of other SOLDIERs. He was often looked up to as being a strong and determined hero by his inferiors. Weilded a long, thin sword known as the Masamune.
Zack

Another successful 1st-Class SOLDIER. His strength accelerated him to the top ranks of Sephiroth and the two became close companions. He has a positive attitude to everything, and while at first glance he seems to have a carefree personality, he's considerate to his allies and has a strong sense of duty.
Cloud

A young Nibelheim boy who aspired to become a 1st-Class SOLDIER in order to prove himself a man to his family and friends - especially Tifa. He failed, and to hide his shame, he became a grunt in the regular army. He's a little shy, reluctant and withdrawn, and often walks in the shadow of Zack and Sephiroth on different missions. The lower part of his face is often hidden by his cloak, or he wears a helmet. He's developed a friendship with Zack.
Others
Aerith

The last of the Cetra, or the 'Ancients'. Her mother, Ifalna Gast, brought her to Midgar when she was very young. A woman named Elmyra found them at the Sector Seven Slums train station while waiting for her husband to come home from Wutai. Ifalna died there, but Elmyra took Aerith as her own daughter. Since then, the Turks have been assigned to keep a lookout for her. They have tried to kidnap her many times, but have thus far failed.
Tifa

A strong young girl who lives in Nibelheim. Cloud is her childhood friend. She was taught martial arts by the great master, Zangan. She became a tour guide for visitors who come to Nibelheim and go rock climbing in the mountains that loom over the town.
Yuffie
Yuffie: A female ninja from Wutai, the daughter of the leader Godo. Shows up in episode 14 - Every Hope and Resolution.
Barret

Barret: Shows up in episode 16 - The Undefiable Muddy Flow of Fate.
Cid

A male Shin-ra Inc. pilot. Shows up in episode 15 - To the Ends of a Distant Sky in the failed rocket launch event recalled in Final Fantasy VII.
Azul
Shows up in episode 4 - Proof of a Scar Filled Existence. Also appears in Dirge of Cerberus. Further details are not known.
Shalua

Details are unknown. She appears in episode 21 - The Preparation to Dive into the Finale. She also shows up, albeit in a much different role and with a much different appearance, in Dirge of Cerberus, as a scientist for the WRO.
Elena

In Final Fantasy VII, Elena is the newest Turk; in Before Crisis, she appears as a high school girl complete with a slightly stylized seifuku. She is Player Character A's younger sister and hates her sister and the Turks because she outdid her.
AVALANCHE
Elfe

A women who was recruited to AVALANCE at a young age for her sword handling capabilities. After having sworn to destroy Shin-Ra, her charisma and fighting capabilities ear . Played a vital role in development and running of AVALANCHE. She is apparently inflicted with an odd illness. It is rumoured she is a decendent of the Cetra like Aerith--this is generally believed to be false. However this theory is backed up due to the fact that Aerith (a Cetra) briefly mentions that she (Elfe) seems familiar.
Sears

The strongest member of AVALANCHE. He had excellent hand-to-hand combat skills and often took charge of executing strategies. He is completely devoted to Elfe and even asks the player character to defend her if he dies in the Reactor (in chapter 17).
Fuhito
The brain of AVALANCHE, he was highly skilled in terms of strategizing and tactical warfare. Armed to the teeth in Machiavellism, he played a rather modest role in helping out the leader in terms ofcoming up with tactical solutions and providing support from a strategic vantge. He however is very treacherous, and has been discussing plans to use Elfe's possible power to their advantage. Fuhito is also shown to have no tolerance for failure as he kills one of his subordinates for being beaten by the Turks.