The Wizard is a pure spellcaster, harnessing arcane and elemental magic to do her bidding. Similar to the Sorcerer and Sorceress of previously Diablo games.
The word "wizard" is used derogatory for rogue Sorcerers and magi that are dangerous to the world at large in the world of Sanctuary.
The female Wizard character in Diablo III is from the island Xiansai, an island to the far north with a culture similar to Asia in our world. Abd al-Hazir writes about a 'wizard' wreaking havoc in Caldeum in his seventh entry of the Writings of Abd al-Hazir.
This female 19 year old wizard was sent to the Zann Esu mage clan, but later handed over to the powerful Vizjerei since she was a "rude and uncooperative student," that the smaller mage clan could not control. They hoped the harsh discipline at Vizjerei "would break her anarchic spirit." Yet even the Vizjerei instructors were unable to rein her in. She was continually being caught seeking out dangerous and forbidden magics without care for herself or anyone around her.
It was rumoured in Caldeum that she ventured into the infamous Bitter Depths below the Sanctum, but the truth is she was caught in the Ancient Repositories, where the most dangerous incantations are housed for the safety of the public.
Valthek, a great Vizjerei mage confronted her and she attacked him. She somehow relied on trickery and deceit to bring Valthek unconscious and then proceeded to flee the city immediately after the encounter. The extensive property damage was decided being the result of Valthek's magical prowess, not the young wizard.
Abd al-Hazir is concerned about the young, rebellious and inexperienced wizard wandering the world, using magics she does not understand. He mentioned that certain schools of magic were too dangerous and "those wiser than you or I determined long ago [to forbid] their practice." Primal forces including time warps include the secrets he suspects she gathered from the Ancient Repositories.
"It is my honest hope that this self-styled wizard chooses never to return to Caldeum."
The above is mostly the background of the female Wizard. Since it's very specifically a woman, we don't know yet where the male version comes from, his background or motivations.
The Wizard is an aggressive archetypal magic wielder founding his powers on the aggressive fierceness of the storm, the arcane and conjuration. Both the male and female wizards are rebellious, headstrong, impulsive, and brilliant. Too smart and arrogant to fit into the authority of the sorcerer schools of the mage clans. Always on the top of their skills and even smarter than their teachers, cocky and self assured.
Some fans have criticized the Wizard for just being the Sorceress with a new look. Jay Wilson commented on that in an interview with 1up.com in December 2008.
- I would respond, "Yeah, you're right; the Wizard is basically a reskinned Sorceress." What we couldn't do with the Sorceress very well was break into what I'd call the old-school pen-and-paper magic user. You know the old magic user who could do a variety of things, like conjure up animals out of midair or create clouds of fog and acid or control time or disintegrate things or use death spells. They had this wide variety of magic that they could use compared to the more traditional elementalist -- which is what the Sorceress is, meaning fire, ice, and lightning -- who was just more limited. What we really wanted to do is break into this area, while if we just did the Sorceress again, we'd be like, "OK, you have to do fire, ice, and lightning, but where does disintegrate fit? Where does slow time fit in?" So we decided [that we'd] just take the same class mechanics, and [that we'd] change the basic concept and name and just have a throwback to that old-school magic user to give ourselves a broader range of magic skills. But there was never a huge desire to go away from the basic gameplay of the Sorceress; there's a lot of repeated skills, and that's intentional.
The wizard skills are arranged into to three distinctive skill tree categories:
All three trees have a combination of active and passive skills. Active skills are used in combat, while the passive skills boost or change the behaviour of the active skills.
The Storm tree skills specialize in the power of the heavens, making the wizard wield electrical energy and casting forth the fierce cold of a blizzard accompanied by the harsh freezing wind. The storm elements also protect and enhance the armour and the power of a wizard.
The Arcane tree skills consists of many classical pen and paper RPGs, including time distortions, Disintegrate, and other magical forces that are not related to elements like Fire, Ice, Lightning. This tree is also good at enhancing or manipulating other spells known by the Wizard.
The Conjuring tree skills summons in protection or offence from other planes of existence. This is where the classic Hydra spell is located, as well as the powerful meteor. The tree can also be used to increase or modify other spells, similarly to the Arcane tree.
The Wizard was the third class revealed by Blizzard, debuting at BlizzCon 2008. It's in essence a re-make of the Sorceress, but with a slightly different set of skills.
You can find pictures in the Diablo 3 screenshot and picture gallery: