The Warlock

With a pseudodragon curled on his shoulder, a young elf in golden robes smiles warmly, weaving a magical charm into his honeyed words and bending the palace sentinel to his will.
As flames spring to life in her hands, a wizened human whispers the secret name of her demonic patron, infusing her spell with fiendish magic.
Shifting his gaze between a battered tome and the odd alignment of the stars overhead, a wild-eyed tiefling chants the mystic ritual that will open a doorway to a distant world.
Warlocks are seekers of the knowledge that lies hidden in the fabric of the multiverse. Through pacts made with mysterious beings of supernatural power, warlocks unlock magical effects both subtle and spectacular. Drawing on the ancient knowledge of beings such as fey nobles, demons, devils, hags, and alien entities of the Far Realm, warlocks piece together arcane secrets to bolster their own power.

In The Nameless Trilogy World

With a staff in one hand, and an eldritch blast in the other, the warlock is sometimes seen as the counter balance to the cleric. While both receive their power from divine sources, they each serve very different purposes. The warlock is on a mission, exchanging the work they do for their patron in exchange for more power. Sometimes these tasks are simple, like a daily ritual or prayer. Other times, they're more specific, like finding a particular item or hunting a particular prey.
In a world where the existence of divine and celestial beings is a proven and incontrovertible fact, the warlock doesn't immediately unnerve people. Some people choose to see warlocks as simple clerics who are perhaps more active on behalf of their patron. After a while though, the unique nature of warlocks and the power that they employ does start to unnerve many people, particularly if that power flows from an unsavory patron. 
The warlock is a versatile choice for anyone who chooses it. They can dwell in the city, in a village, in the wilds, or anywhere in between. For the warlock, what matters is the service that they render to their patron. So less than what your warlock character wants, what instead does your patron want? This will require conversations with your Dungeon Master, who will implement your patron's motives and ideals into the campaign. How does your character relate to your patron, and how does this relationship affect how you view/treat others?

Resources:

• Player's Handbook
• Xanathar's Guide to Everything
• Xanathar's Lost Notes to Everything Else

Subclasses:

• The Archfey (PHB)
• The Fiend (PHB)
• The Great Old One (PHB)
• The Celestial (XGtE)
• The Hexblade (XGtE)
• The Chaos (XLNtEE)
• The Noble Genie (XLNtEE)