Does a warlock have to know his patron?

Question

I'm in a game that has a lot of first-time players (myself included) however the person I am questioning I do not believe is a first time player.

We've been playing for about 6 months now (October - Present) though our Warlock was gone for the winter quarter and missed the previous arc (nbd). I didn't know a lot about DnD when we were playing in the fall but after winter quarter I had a better sense of what well, made sense in DnD. And I noticed some...odd behavior from our Warlock.

The main thing I noticed that was fishy is that after an incident where we (accidentally) killed his familiar (an imp) he claimed it was a messenger from his patron (fair enough). I asked him who his patron was and he said "I don't know who my patron is" which isn't right, isn't it? I asked out of character because I thought they had to choose and my DM was like "yeah they don't know where their magic comes from" but i looked it up and the choices in the Players Handbook were "the Archfey, the Fiend, or the Great Old One," which all have specific boons.

Does a Warlock then have to know his patron, or can he just not know it? Will he miss out on his boons?

Answer 1

Not Necessarily

Nothing in the text requires a warlock to know his/her patron's specific identity.

you have struck a bargain with an otherworldly being of your choice: the Archfey, the Fiend, ...

The only thing you chose is the type of being, not the entity itself. That is worked out with your GM.

Here's an excerpt from the Great Old One patron to show how this relationship might work.

Your patron is a mysterious entity whose nature is utterly foreign to the fabric of reality ... The Great Old One might be unaware of your existence or entirely indifferent to you, but the secrets you have learned allow you to draw your magic from it. 

In this case, not only would the warlock not know the patron, it's possible the patron doesn't know about the Warlock.

So while his character may know what type of entity (Fiend, Archfey, etc.) fuels it's magic, he doesn't have to know what individual specifically.

The GM probably knows

Sometimes the GM will keep some things about a character secret even from the player so the player can learn more about his character as the game goes on. This can be fun for some people who really enjoy getting into the role of their character.

I wouldn't worry too much as the flavor isn't that important for gameplay purposes.

Answer 2

The question is interesting. I will start with

• What does "Not knowing its patron" mean?

If we read p. 108 from PHB, the section about the patrons say

The beings that serve as patrons for warlocks are mighty inhabitants of other planes of existence - not gods, but almost godlike in their power. Various patrons give their warlocks access to different powers and invocations, and expect significant favors in return.

From that, we expect some kind of interaction between the Warlock and the Patron. The introduction says this relationship can be like that of a cleric and a deity, but mostly are like that of a master and apprentice. In p. 107, this relationship is further clarified as

you have struck a bargain with an otherworldly being.

So far, the Warlock should know his Patron - he made a pact with it, after all, and draws his powers from it, while acting in behalf of it, although as noted in David Coffron answer, that doesn't always apply.

But now back to my question: what does "not knowing it" mean? The Warlock might have done a pact with "a fiend", but not necessarily knowing WHICH fiend. The Warlock might have done a blind pact, without even knowing with what kind of Patron. It could just be a shadow that talked to him when he made a ritual, but without a shape or revealing itself. If the Warlock is good and would only serve to the Archfey, maybe a Fiend actually pretended it was an Archfey to manipulate the Warlock?

Also, remember: the Warlock said he doesn't know, that doesn't (necessarily) mean he actually doesn't know, he might just be lying to you. Honestly, if neither the DM or the player are seeing a problem on it, I wouldn't go as far as telling someone he's playing his character wrong, after all you don't have all the info on him, only him and (maybe) the DM do. (Please don't take it the rude way)