From Destinypedia, the Destiny wiki
Warlocks are a class of Guardian who are best described as "warrior-scholars,". They utilize their Traveler-given powers for both attack and defense. Warlocks specialize in ranged melee attacks and cast elemental spells to eliminate their enemies. They are also adept at offering support to fellow Guardians and fireteam members, by healing them and enhancing the strength of their weapons, and are just as comfortable fighting from mid-air as on the ground.
Warlocks were the first to tap into the power of the Traveler, wielding its Light as they ventured beyond the safety of the Wall. They know that each discovery offers new possibilities, and they have devoted themselves to understanding the Traveler, its power and how to better channel it. A Warlock's mind is an arsenal of deadly secrets, balanced between genius and madness. On the battlefield, those secrets can seem to shatter reality itself. They search the frontier to find a means to defeat the Darkness once and for all.
Warlocks are known for pushing the boundaries of knowledge, even into dangerous territory. At least two warlocks, Toland, the Shattered and Osiris, were exiled for studying the Hive and Vex too closely. There also exists an order of warlocks called the Thanatonauts, who take advantage of Guardians ability to resurrect themselves to receive visions every time they die.
All Guardians have certain abilities, many of which are granted by the Traveler, others which may appear more mundane in nature. All Guardians also have a "double jump" ability, as well as a "grenade-like" ability whose effects vary by class and subclass. All these abilities with the exception of the double jump were able to be upgraded over time in the past, and can be used in competitive PvP.
List of appearances