Though employed by S.I.N., in reality Crimson Viper is a secret agent under the employ of a U.S. government agency (presumably the CIA) investigating the BLECE project while assassinating a select group of targets. It is revealed through her story that her target is Seth, one of many constructs designed to serve as an unstoppable army for M. Bison, in addition to the fact that he is number 15 of a presumed 41 others (assuming she is killing them in order; this is never confirmed). In addition to assassinating Seth, she's also to acquire the data on BLECE and turn it over to her employers after the tournament. Unfortunately, the data pertaining to BLECE is destroyed by Cammy before Viper has a chance to copy it, resulting in several years of investigation disappearing into thin air. The data linking Shadaloo to S.I.N. is not destroyed, however, and is recovered by Chun-Li prior to the facility's destruction.
Crimson Viper wears a specially designed Battle Suit for the tournament, developed and manufactured by S.I.N.. When inquired by an Executive as to the reason for her participation in the tournament, she states that she's the only test subject to utilize 100% of the suit's capabilities effectively, and thus is the prime candidate for the field test. The suit is remarkable in the sense that it resembles an ordinary business suit, though two weapons lurk within the accompanying gloves and boots.
The gloves have metal knuckles that can be electrically charged, creating visual arcs of electricity when enough power is supplied; these can stun or damage an opponent quite heavily at higher settings, which combined with Viper's natural speed and agility pose an incredible danger to fighters of all skills and sizes. The boots hold jets inside the arc between the heel and sole, with a switch on the side of the boot activating the temporary jet propulsion. The boots are capable of granting the wearer a much greater jumping ability, though Viper usually fires them up and uses them in a defensive kick, burning anyone within distance.
The suit does not provide the wearer with any sort of ranged attacks or abilities in the traditional sense. However, the gloves, when switched to a particular setting, allow C. Viper to unleash the "Seismic Hammer," an explosion from beneath her opponent that she causes by punching the ground. A very deceptive attack considering it travels beneath the floor. The Battle Suit does not (presumably) protect the wearer from damage; it was designed for stealth and ease of concealment, not battlefields or war zones.
Crimson Viper's working personality is superior and condescending, as seen in her interactions with Chun-Li, Cammy and Hakan. However, she is also genuinely interested in the inner workings and problems of the other fighters and dose not like hurting good or defenless people.
C. Viper appear in UDON's Street Fighter IV comic which focus on the game's newcomers (herself included).
She also appears as a playable character in Marvel vs. Capcom 3: Fate of Two Worlds and its updated version, Ultimate Marvel vs. Capcom 3. in her ending Nick Fury (from the Ultimate Marvel Comics continuity) shows up at her darkened apartment just as she's getting home and offers her a job in working for S.H.I.E.L.D.
- C. Viper's suit and moves closely resemble those of Captain Commando.
- C. Viper is the first playable female character from the United States in the series.
- She is the only playable mother in the Street Fighter series.
- It is still unknown if Crimson Viper is married, divorced or possibly a widow.
- The Super Street Fighter IV website lists her birth date as July 18, and the Marvel vs Capcom 3 site lists her age as 30.
- Viper's second alternate costume, the skin-tight battle suit, features a logo around the chest area incredibly similar to that of the real-life CIA.
- C. Viper is the only playable character from SFIV not to make a direct cameo appearance in Street Fighter X Tekken; Abel and Rufus are playable, and El Fuerte appears on a billboard in the background of one of the stages. However, Tekken's Jin Kazama dons a battlesuit similar to Viper's as one of his Swap Costumes, and Viper herself is referenced in the Playstation Store/Xbox Live Marketplace descriptions (and the Japanese website).