Before the War
Little is known about Whisper before the war between the Resistance and the Eggman Empire, but it is apparent that she had some sort of traumatic encounter with Dr. Eggman at some point before the war. (StH: #8)
During the war, Whisper aided the Resistance from the shadows, often turning the tides of battle and saving the lives of many Resistance fighters, including Silver the Hedgehog. Despite her efforts to thwart the Eggman Empire and support the Resistance, she never officially joined the Resistance, nor even revealed herself to them. Because of this, she became something of a legend on the battlefield and became known as the "Guardian Angel of the Resistance". (StH: #8)
For unknown reasons, Whisper infiltrated an Eggman base at the same time as Sonic did and secretly assisted him from the shadows. First by jamming a security gate with a spike ball before it closes, allowing him to pass, then by taking out a giant Spina that Silver had failed to completely incapacitate. (StH: #8)
She then found the subsequent security gate already sealed and set about breaking through it with her Variable Wispon, using several of its modes to no avail. Sonic and Silver soon arrived and attempted to make contact with her. Startled by Silver's overbearing greeting, she retreated to the rafters using her wispon's umbrella-like, green hover mode. After Sonic apologized and introduced himself, her Wisps emerged and greeted Sonic. Reassured by Sonic's more tactful approach and her Wisps' warm response to him, she hesitantly emerged, removed her mask, and introduced herself as "Whisper", which Silver mistakenly took for a request. (StH: #8)
Silver opened the final security gate revealing E-107 Theta and a host of Spinas, which Whisper engaged in battle along with Sonic and Silver. She unleashed a powerful orange rocket blast incinerating several badniks and nearly hitting Sonic. Using her wispons's green hover mode once again, she respositioned herself upon a high perch and zapped Theta in the head with an azure laser to little effect. Theta returned fire, obliterating her perch and sending her crashing to the ground. Trapped under a pile of scrap, Whisper was helpless against an onslaught of encroaching Spina. Her Wisps emerged, eager to defend her, but Silver intervened before it was necessary for them to attempt to fight, freezing the badniks and launching them into a wave of missiles launched by Theta. Silver then freed her from the rubble using his psychic abilities and helped her to her feet. In reference to her Wisps, he commented that she had built quite a team, and that he would be honored to be part of it. Whisper replied with a bashfully undecided, "Maybe." (StH: #8)
As the heroes regrouped, Whisper then spotted a terminal with a prominent Eggman Empire symbol displayed upon it and became enraged, setting off to smash it with her wispon's hammer-like, blue cube mode. When Sonic frantically asks her to wait at least until after they have secured the vital intel stored within it, she takes it quite harshly, agreeing to stand down, affixing her mask, and withdrawing into the background as Sonic and Silver warned the Resistance of Neo Metal Sonic's true plans. (StH: #8)
The Battle for Angel Island
Whisper was among the various heroes who allied with the Resistance in the effort to take back Angel Island from Neo Metal Sonic. She was assigned to Team 2 for the assault by Amy Rose, along with the bulk of the Resistance fighters. On the voyage to Angel Island, Sonic thanked her for aiding them despite her aversion of crowds and asked her to stay safe during the battle. She affirmed and reciprocated his sentiments before he left to give her space. Spotting Shadow across the room, she glared angrily at him across the room without him noticing. (StH #9)
When the battle began, she evacuated the ship with the rest of Team 2 using her wispon's green hover mode. Landing on the western shore, she was commanded, along with Tangle the Lemur, to cover Tails while, "He did something smart." (StH: #9, #10)
Whisper is a rather mysterious individual who manifests a rather shy and timid personality. It is heavily implied that she has experienced some past trauma, likely at the hands of Dr. Eggman, that has lent to this. While she is extremely fearful and mistrustful of other people, she exhibits a strong bond with her Wisps, as illustrated by their reception of Sonic persuading her to trust the hedgehogs, and the Wisps willingness to stand up to the badniks in order to defend her. Likewise, her enraged response to the terminal bearing the Eggman Empire symbol and her pained response to Sonic's rather reasonable request to wait shows the tell-tale signs of someone who has experienced repeated abuse (StH #8). It would seem she also hold an unknown grudge against Shadow. It is currently unknown what the nature of this disdain is or whether it is related to Eggman.
It is currently unclear how much of her personality is a result of this past trauma or a naturally introverted disposition. Whatever, the truth may be, it has lead her to be a literal "Lone Wolf", preferring to do her own thing and work on her own rather than cooperating directly with others. This is illustrated by the fact that while she assisted the Resistance during the war, she never actually joined or even revealed herself to them. Moreover, during the battle with Theta, she nearly blasted Sonic with her orange rocket attack, showing inexperience in coordinating with others strategically (StH #8).
Nevertheless, she opens up, ever so slightly to Sonic and Silver after their initial encounter, perhaps building bonds with other people for the first time since the trauma and creating hope for further recovery and growth (StH #8). She trusts Sonic enough to come directly to the Resistance's aid for the first time rather than working from the shadows in the Battle for Angel Island (StH #9).
Whisper is an anthropomorphic wolf with biscotti colored fur, a cloudy white "mask", and a brown muzzle. She wears her hair in a pony tail held together by a black hairband with bangs swept across her right eye. Her eyes are cadet blue, although they are often closed to the point of squinting. She has thick black lashes and grey eye shadow. Her fangs protrude from her mouth which is often in a natural frown. She often wears an ornate mask which she not only uses for targeting purposes, but to hide behind. She has a bushy tail which ends in several tufts of fur sticking out in various directions.
She is 100 cm (3'3") tall and wears an outfit geared towards combat utility including: black elbow and knee guards, black steel-toed combat boots, black clawed gloves with grey palms, a beige strapless top, grey pants, and a black cloak.
Whisper is an expert marksman, able to infiltrate and eliminate targets without being detected by friend or foe alike. Her natural aptitudes are further enhanced by her unique equipment. She seems to prefer positioning herself on high perches and snipe enemies from a safe distance, but is able to hold her own in melee combat as well.
- Variable Wispon: Whisper wields a unique wispon of unknown origins that is able to switch between various Wisp powers by loading different Wisp canisters into it.
- Azure Laser: Fires a powerful laser beam.
- Orange Rocket: Fires a powerful explosive blast.
- Green Hover: Transforms into an umbrella allowing her to float up or down quickly.
- Blue Cube: Transforms into a large hammer.
- Purple Spike: Fires a spinning spike ball.
- Mask: A mask Whisper uses for targeting. It covers her right eye and assists her left eye in aiming.
- Cloak: A utility cloak Whisper wears over her shoulders. It stores up to 6 Wisp canisters within it, 3 on each side.
- Wispon Canisters: Specialized cartridges that store various Wisps to be loaded into Whisper's wispon.
- Whisper the Wolf was created by writer Ian Flynn and designed by Evan Stanley.
- Whisper is the 4th new character exclusive to IDW Sonic the Hedgehog and the 2nd new heroic character.
- Whisper's mask is inspired by Japanese Kabuki masks.
- Whisper was officially revealed at the Sonic the Hedgehog's Way Past Cool Panel at SDCC 18 on July 19th, 2018. 
- Whisper's early designs were somewhat different than the final version.
- She had blue hair and fur.
- She had a more ostentatious costume.
- She did not originally have her iconic mask.