The Death Knight is the first Hero Class in World of Warcraft. All races can be Death Knights.
The Death Knight will have three presences they can choose from at any time (similar to stances) to best fit their current task. They are as follows:
Blood Presence: Increases damage done by 15% and heals the Death Knight by 2% of damage dealt. Only damage dealt to targets that grant experience or honor can trigger this heal.
Frost Presence: Increases armor by 60%, increases health by 10%, reduces spell damage taken by 5%, and increases threat generated by 45%.
Unholy Presence: Increases attack speed by 15%, increases movement speed by 15%, and reduces the global cooldown on all Death Knight Abilities by 0.5 sec.
Now we will dwell on the unholy talents of the death knight.
Vicious Strikes
Unholy talent points required: 0
Description: Increases the critical strike chance by 3% and the critical strike damage bonus by 15% of your Plague Strike, Death Strike, and Scourge Strike.
Morbidity
Unholy talent points required: 0
Description: Increases the damage and healing of Death Coil by 5% and reduces the cooldown on Death and Decay by 5 sec.
Anticipation 
Unholy talent points required: 0
Description: Increases your chance to dodge by 1%
Epidemic
Unholy talent points required: 5
Description: Increases the duration of Blood Plague and Frost Fever by 3 sec.
Virulence
Unholy talent points required: 5
Description: Increases your chance to hit with your spells by 1% and reduces the chance that your spells and diseases you cause can be cured by 10%.
Unholy Command
Unholy talent points required: 5
Description: Reduces the cooldown of your Death Grip ability by 5 sec and the cooldown of your Demand ability by 1 sec.
Ravenous Dead
Unholy talent points required: 5
Description: Increases the total Strength of you and your Ghouls by 1% and reduces the cooldown on Raise Dead by 30 sec.
Outbreak
Unholy talent points required: 10
Description: Increases the damage of Plague Strike, Pestilence and Blood Boil by 10%.
Necrosis
Unholy talent points required: 10
Description: You auto attacks deal an additional 5% Shadow damage.
Corpse Explosion
Unholy talent points required: 10
Description: Teaches the Death Knight spell Corpse Explosion.
On a Pale Horse
Unholy talent points required: 15
Description: The duration of all Stun and Fear effects used against you is reduced by 10%, and your mounted speed is increased by 10%. This does not stack with other movement speed increasesing effects.
Blood-Caked Blade
Unholy talent points required: 15
Description: Your auto attacks have a 5% chance to cause a Blood-Caked Strike, which hits for 50% weapon damage for each of your diseases on the target.
Shadow of Death
Unholy talent points required: 15
Description: Increases your total Strength and Stamina by 2%. In addition, whenever you die, you return to keep fighting as a Ghoul for 45 sec.
Summon Gargoyle
Unholy talent points required: 20
Description: A Gargoyle flies into the area and bombards the target with Nature damage modified by the Death Knight's attack power. Persists for 1 sec per 8 runic power up to 1 min.
Impurity
Unholy talent points required: 20
Description: Your spells receive an additional 5% benefit from your attack power.