In the past, I've almost always had at least one NPC that would travel with the characters as a type of "lore master" to expand on the story. I've tried to make the character witty and, once the characters have sufficient information, inevitably pulled from the party.
Is there another way I can inject plenty of lore about the "world"/campaign without it directly coming from the DM or my DMPC?
"Show, don't tell" is always the most relevant advice. If the background is important at all, then it should surface in the real world via books, statues/ruins, cultures and common sayings, etc. You know, how we find stuff out about our world and real life. Instead of infodumping, have it come in from various directions - someone shooting the bull in a tavern, an old lady met on the road, an abandoned shrine with an inscription, a couple books in a murdered mage's satchel. Any schooled PC, you can give some of it to them as "Well, you know from back in the Academy that the Knights of Northrop always ride black horses because..." Look for relevant knowledge type skills on the PCs' character sheets as a channel for that. Since you're using somewhat archaic language I assume you mean in a medieval fantasy type game but of course in a modern or future game you have TV, Internet, and ninth grade history class to add to the mix.
I would be concerned with the "pet DMPC" approach because it seems like it would tend to discourage PCs from actually exploring and trying to find out information, out of the assumption that relevant info will be dumped on them. Make them piece it together, seek out sages or other people that might know something, etc. Converting a party into proactive mode always engages them more and gives opportunity for plot hooks/quests.
Also - if it's not relevant to the plot at hand, take a light hand with it. I know, as a DM I want to get across the Many and Varied Wonders of my Campaign World (tm) too, but DMs tend to want about 300% more of that than the players do. I sometimes prepare a world/campaign briefing sheet for my players ahead of time to convey lore they should all just know, and have learned the hard way that if it's more than a couple pages they're not going to read it.
I have a wiki for my campaign. And most pages contain a section on, 'What is common knowledge'. Yes, you end up rewarding your PCs who do their homework, but by doing this, you will be amazed at the depth of knowledge some PCs get... as well as the amount of new data you will get answering their questions about these pages.
I recommend doing this because this allows them to steep themselves in the knowledge you wish them to have on their own time, not game time. Make sure you include the laws of the area in this page, or somewhere. This one is important.
During character creation, be very complete in the factions and family the PCs come from. Again, every possible faction should be clearly written about and the PCs should be able to read up on what the relationship their guild, church or faction has to the the area and the world.
Part of understanding the world and setting you create is in making the PCs understand their place in your world. Make sure you have these factions clearly designed and prepared ahead of time. I know you are asking how to inject it, but giving the PCs a place to stand gives them a piece of the puzzle ahead of time.
Have a broadsheet or the like available for daily reading, and make sure you do up some ahead of time. Let the players every day find out about the world through your work and words. This allows you to inject foreshadowing and important information you wish them to have.
Use Microscope to collaboratively build your world's history with your players. Then, more people can make more subtle references to events without having huge and boring expository dumps.
Another interesting way is to have fixed-point time-travel (or flashbacks) and allow your players to engage as people of history.
Have players submit backgrounds or plot hooks related to their characters. Take the people, places, and things from those ideas and build them into your game world. Work on what the players tell you and add a few elements from your own imagination to keep things interesting. The players get a sense of involvement and importance in ongoing events in your game world.
Have you looked at Apocalypse World? In that game, when you try to find out about something (similar to a Knowledge(X) or Spot check), you get to ask the GM questions, who answers them truthfully. The questions are all listed out, you have to ask off the list. The great thing is, these lists are really aimed at bringing in elements of the setting. Stuff like "Who's in control here?" or "Where's the best escape route?" Questions like that really prime the GM for answers like "The Cult of Kul-a-thul has ruled the steppes for as long as anyone can remember" or "The planes kingdoms always included an escape tunnel to the nearest body of water in their castles."
The best part is, since it's player-initiated, they're already invested in the answers. And, even better, it helps make sure that the GM's only providing information that's actually useful and interesting.
You could adapt the same concept to any number of games. In d20 I'd probably write lists for Spot, Search, and Knowledge. Hit the DC, you ask one, for each 5 over, you get to ask one more.
Something you could look at is the collaborative world building offered in FATE games, such as Diaspora for Sci-Fi and Legends of Anglerre for Fantasy. All the players are involved in creating the base setting, so they already know a fair bit about it and have some ideas that they haven't shared. FATE also includes a mechanic for players introducing information, either casually or through the use of FATE Points.
This latter bit allows things to be really organic, because otherwise having the loremaster travelling with the characters makes the most sense if the characters are from a different world (or different part of the world), and the NPC is literally a friendly guide. That's one of the reasons CRPGs make use of amnesia (cleverly done in Final Fantasy VIII, not so well done in other games) or being thrust into a new world (obviously done in Final Fantasy X, not quite as obvious in Tales of Vesperia, but also using a loremaster character).
If the characters are from the world, they shouldn't need someone to tell them what's already known to them. You could get around this by telling certain players OOC what their character knows about a particular situation, and let them exposit how they see fit. This usually leads to GMing techniques like taking the player aside or passing notes, but it's not something I'm personally fond of. Hiding information can be interesting and add to the sense of adventure, but I think it should be used sparingly, rather than as a primary method of adding spice to the story.
The depth of lore and details of the world are (for some people) what makes the world engaging. As worldbuilding DMs we love to craft extravagant histories and complex lore to fill our world. This is all a waste of time if we fail to get our players to buy in to our world. We need them to care about the history and its people or the lore won't matter too them.
There are many ways to do this and they will vary between systems and DMs, I don't pretend to be an expert in all of them but this is some of the ones I have used successfully in my own campaigns.
Including your players in the process of worldbuilding is the fastest way to get them to learn the lore, they helped write it. This method has the added benefit of reducing the workload on the DM.
In my campaign I do this by allowing my players to create their own home towns, complete with culture, history and NPCs. I ask them for at least half a page of writing and then ask additional questions to help fill out the town. I then place these towns on my world map and allow them to dictate the surrounding regions; small rural towns necessitate a wilderness region, large capital cities become major trade locations.
I also allow them to influence how their chosen race is seen in the world. For instance I had a dwarf players who came up with how the dwarf society was structured and how they interacted with the other races. I adapted this slightly to fit into the campaign and that player was instantly an expert on her own race.
Once my players have established their backgrounds and home cultures I use them to assess what parts of the worlds lore they would be aware of. When parts of the lore become relevant I prompt the appropriate player to make a knowledge of the relevant type. I don't use a fixed DC for this but instead the higher they roll the more information I give them.
I always make reference to where the character learned the information, the wizard learned in in his years of detailed study, the bard in the folksongs they sang as a child, the street urchin overheard it in the alleyways they grew up and in and the noble learned it from an old wise uncle. Whatever the source I make it relevant to the characters backstory. This helps to make the players feel their backstories are actually important meaningful choices and that will affect the information available to them in the game.
It is important to share these rolls around and not just give them to the players with high intelligence. Sometimes the half-orc with a 6 in intelligence will know more than the wizard simply by having lived through it.
At the start of campaigns it is important to prepare your players on the world they are entering. I will often give a detail exposition of the world during session 0, this helps in getting characters that fit the theme better. Sometimes players will express an idea during this session that you can incorporate into the campaign.
You can boost this by sending out world primer handouts ahead of time to prospective players and only bring in those that are interested in the world. By canvasing more people and only bringing in the players interested in this campaign specifically you have already avoided a lot of issues with player buy in down the line.
Between each session of my campaigns I write up a short exert of between 50 and 500 words. Sometimes this will be humorous retellings of the best moments of the last session, sometimes I use it to express things from the bad guys or another NPC's point of view, adding extra dimensions to these characters. Whenever I can though, I use this to inject additional lore into my campaigns. I lay hints and clues about grander scheme of things, linking the dots the players missed.
At the start of the next session I read this aloud to my players. This ensures they have at least heard it once and helps to set the scene and mood at the start of the night.
When traversing the tunnels below an old city the players find writing in a form they don't understand, though the symbols seem very similar they are more archaic in form. When traveling across the desert the find the ruins of a city long past, the same runes mark the stonework here.
If your lore contains a precursor civilization show it in the world they travel through. There will always be artifacts and architecture left behind. New cities are built atop the old, but there are secrets to discover below for the brave souls willing to find them.
My current campaign features a dominant and tyrannical dwarven empire that was overthrown hundreds of years earlier. The history of distrust however is still evident throughout the world. Dwarfs are hated throughout large parts of the world and I ensure my players feel this (I cleared it with only dwarf player ahead of time). Though the empire itself it gone evidence of dwarven architecture and influence can be found in all corners of the world. This has worked so well to get my playing interested that our next campaign will be set 100 years before the fall of the empire.
Sometimes there is a particular piece of lore that is relevant but none of the players would have reason to know it. In these situations I introduce an NPC to educate the players. After earning the players trust the character says something like "Do you know the story of....?" this has always been enough of a hook for my players, provided you keep the story short and interesting.
Other times the law can play out through the character arc of an NPC. I have a religious order that cuts of hands of those they expel. I introduced the law though one of the victims, the players helped him get vengeance and learned of a powerful order in the process. Win-win.
The lore of the world should inform and drive the story, a story that is being played out by the players. So you need them to want to play out the lore of the world. Connect the lore directly to the players backstories, make it personal and useful and they will seek more. Lace hints of the past throughout the present, make them obvious and your players will take note. Use NPCs to fill the gaps and answer the players questions.
If done properly by the end of the campaign your players will know your world almost as well as you do. And by making them care about the world, that world ending epic level threat at the end of your campaign means so much more.
