Canon:Warlock

With powers derived from a supernatural bloodline, Warlocks invoke magic by using just the power of their will. Through these invocations Warlocks perform supernatural feats and create blasts of eldritch energy to destroy their opponents. While these powers are the legacy of an ancestor's pact with fey or extra-planar forces, the Warlock is free to follow his or her own path to glory or infamy.

3.5e
Introduced in Complete Arcane, Warlocks introduced the concept of Invocation as a class ability component. Their most memorable class feature is the eldritch blast, an invocation they obtain at first level that does more damage with increased level. Many invocations modified the eldritch blast, either changing the shape or adding an effect.

4e
One of the original base classes featured in the Player's Handbook 4e, a Warlock is a Striker that curses its opponents, causing them to take additional damage from its attacks. Depending upon its pact, a Warlock receives a boon whenever it reduced an opponent to 0 hit points.