Shiva

Shiva is a frequently recurring summoned monster that usually takes the shape of a blue woman. Her signature attack is "Diamond Dust" (sometimes called "Gem Dust"), which is a burst of Ice/Blizzard magic. Though Shiva shares a name with the Hindu god (also known as Śiva), the two beings have little else in common, and it is believe that the Final Fantasy Shiva is so-named because the similarity to the word "shiver."

Along with Ifrit and Bahamut, she is one of the only summons to appear in every main series game from Final Fantasy III through Final Fantasy XI.

Biography
Although enjoying regular appearances throughout the series, Shiva, like most of the popular summonable entities, has never been given any significant backstory. Shiva has occationally been shown as one of the more 'friendly' summonable entities. Whereas most others maintain a particular indifference to the player or, often, initial hostility which must be subdued by defeat in battle, Shiva has never been portrayed as an antagonist to the player's party. In Final Fantasy VIII for example, Shiva demonstrated a clear affinity for the main protagonist.

Physical appearance
Shiva's basic physical characteristics are that of a willowy human female with extremely pale skin and long, blue hair to invoke an image of ice and cold. This image is reinforced in later summon sequences by the addition of arctic winds, freezing temperatures and large ice crystal formations. Despite the cold, Shiva invariably wears only enough clothing to conceal her modesty, along with boots and other minor aesthetic pieces. She carries no weapon, and implements her main Diamond Dust attack with arm gestures and/or force of will. Later games in the series allow Shiva to carry out physical attacks in the form of kicks and punches.

Final Fantasy III
Can be summoned by both Conjurer and Summoner job classes.

Final Fantasy IV
Appears as a summon (or "call" in the first North American version) for the character Rydia after she rejoins the group in the Underworld.

Final Fantasy V
The Summoner job class has ability to call her. She is obtained in a tower behind Worse Castle.

Final Fantasy VI
Appears as an Esper, first encountered by the Returners in the Magitek Factory of Vector. After being drained of her power, she and Ifrit are disposed of by Kefka in a waste chute. Believing they mean the two Espers harm, Ifrit attacks the group. Shiva soon senses Ramuh (Final Fantasy VI)'s power within them, and halts the battle. They then grant their abilities to the Returners. She teaches the following spells:
 * Ice X10
 * Ice 2 X5
 * Osmose X4
 * Rasp X4
 * Cure X4

Final Fantasy VII
Shiva materia is obtained on the beach of lower Junon after Cloud and company defeat the boss Bottomswell. She can then be assigned to a weapon or armor, and called upon in combat.

Final Fantasy VIII
Available as one of two Guardian Forces assigned to protagonist Squall Leonhart at the start of the story. In keeping with Final Fantasy VIII's Junction System, GFs may be assigned freely to any party member.

Final Fantasy IX
According to notes left on the Summoner's Wall at Madain Sari, the Eidolon Shiva was first discovered by summoners in the form was that of a small child. As years passed she eventually grew into her more familiar and adult appearance.

Final Fantasy X and X-2
The Aeon Shiva's manifestation in this game is the result of dream-imagery provided by a Fayth (the sentient spirit of a dead person). Summonable entities in Final Fantasy X came under player control for the first time in the series, and replaced the player's own party members when called into battle. Aeons possessed a number of new unique attacks alongside the ability to attack and use items and magic, and could carry out their traditional main attack via the Overdrive system. Shiva reappears as a Dark Aeon the Gullwings must fight in Final Fantasy X-2.

Final Fantasy XI
The job class Summoner can unlock the "spell" Shiva upon completion of a certain quest.

Final Fantasy Tactics
The job class Summoner earns this ability over time. Her Diamond Dust attack is a large ice elemental attack that spreads over a portion of the battlefield.

Final Fantasy Tactics Advance
The Summoner job class learns the ability to summon her through the Snake Staff item. Unlike in her other appearances where she appears scantily clad, this incarnation of Shiva is shown in full armor with only the bottom of her face revealed.