The Chronicon ( new lore book ) is probably my favorite to date. Pretty much the first part of the book deals with Calus’ past, most of which was already known.
In section called DCCII, Calus is stewing while thinking about his dead Shadows ( who had all died to Ghaul ), when he is told that Ghaul was killed by a Guardian. Calus immediately makes plans to meet the guardians, he also makes robotic clones of himself, which we saw in the original Leviathan raid.
A later section, DCCCVII, Calus is shown future events by the tetrahedron ships. Apparently, The Guardian ( us ) becomes the Shadow of Shadows, and Calus hosts a huge banquet for the event.
Section MCXII is where it gets really interesting, but also improbable. The Guardian is asked to gather an Army of Shadows, and first we go to Mithrax, who accepts our offer. With him we kill a bunch of Fallen. We then go to Mara Sov, who does not accept, thus, we kill her. We then go to Petra, who accepts, and with her we slaughter the Awoken. Note: Mithrax is later killed in battle outside the Inner Sanctum.
Section MCXX is probably my favorite. The Vanguard and Rasputin are threatened by Calus and his growing number of Shadows, they ask him to remove his presence from the planets and moons his forces are on. The Guardian is sent to meet with the Vanguard to discuss peace, they deny and choose war with Calus. The Guardian, angered by this, responds interestingly: “Who do you think I am? Without me, you have only a dwindling army of ambivalent soldiers. I am the Young Wolf. I killed the Taken King. I defeated Ghaul, roused the Traveller, I silenced the Moon. I stopped the invasion. I broke the curse, I broke the Houses, I killed the Queen! I am the Shadow of Earth!”
Quite a few interesting things with this statement from our guardian. First, we actually said something, that’s pretty cool. Second, it says we broke the curse, so in the future we do finally break the Dreaming City curse. Also, if this in order of events, then the “invasion” hasn’t happened, and we haven’t silenced the Moon yet, this might be alluding to the next year in Destiny 2, where we apparently go back to the Moon. Just some of my thoughts on this dialogue.
The Guardian then invades the Hellas Basin and attacks Rasputin. The Vanguard begs for mercy, but we deny them.
Later in the book, Savathûn enters the scene. A rift opens in the Leviathan and she and her horde of Hive crawl out. But what’s really interesting is a quote from Calus: “But the great emperor Calus had seen Death at the edge of the universe and was not afraid, for this witch and her spawn were not Death.”
This completely silences the discussion of who’s in the tetrahedron ships. It’s the Darkness, not Savathûn. What comes next is really boring because basically we singlehandedly kill her and her spawn.
The book ends with MCVLIII, which is an affectionate letter from Calus to The Guardian about how much he cherished his time with us.
Just thought I’d kind of summarize the book, it’s very interesting and there’s so many fun details throughout.

Also, just thought I’d point out that Calus often says “o champion mine” to us. That is no coincidence.

I still need to get to reading so much of the back catalog so these are helpful!

The 'things yet to pass' were written by Calus' scribes and are full of errors, misunderstandings, blandishments, and propaganda. You can't take them as accurate predictions of what will happen.

Indeed.

It's especially useful to compare the tone and description of events in The Chronicon to it's companion lore book in this expansion, Confessions.

The end of Confessions is especially interesting, in that it positions Calus as a possible in-game avatar of Bungie, or maybe the lore author?

Indeed.

It's especially useful to compare the tone and description of events in The Chronicon to it's companion lore book in this expansion, Confessions.

The end of Confessions is especially interesting, in that it positions Calus as a possible in-game avatar of Bungie, or maybe the lore author?

Haha, I would not want to think Calus is my avatar.

My favorite part was the Zavala vs Hawthorne chapter:

Thus did the Shadow of Earth slay the Titan Vanguard Zavala.

As recorded by the enshrined Scribe Shagac, the Vanguard of Earth requested mercy, and their request was denied. Thus the Titan Zavala was permitted a final day to consider his perfidy before his death.

So the Titan Zavala went to the Human known as Suraya Hawthorne and said, "Suraya Hawthorne, will you play a game of checkers with me?"

Suraya Hawthorne agreed, and so the two played twenty-seven games of checkers, and listened to the music of bagpipes and synthesizers, and dined upon Earth delicacies such as nuggets of chicken and the beer of roots.

"Titan Zavala," said Suraya Hawthorne as Earth's sun rose upon their latitude, "There will never again be a checkersmaster of your like."

"No, Suraya," said Titan Zavala. "You must become a greater checkersmaster than even me, if you are to lead the resistance."

Thus the Titan Vanguard did not meet his final death alone. And Suraya Hawthorne was slain at a later date.

Over and over in the previous parts of this ongoing wacky made up story, one of Calus' scribes had been correcting and scolding the other one for inaccuracies and over the top fictions... but here, and this is the best part, here the more senior scribe says about this part:

^ Note to Underscribe Shipal: Very good. This is entirely credible.

There's some other interesting stuff in this book:

A little more about the strange creatures that can neutralize Light that the Drifter once found on a strange moon.
An epic, Mars shattering battle between Ikora Rey and our Guardian.
Cayde-7.
The many, many, uncountable deaths of Guardian Uldren Sov.
Our Ghost's final words.
And many other pieces of completely made up nonsense that was very confusing to read until I realized what was actually going on. :)

The 'things yet to pass' were written by Calus' scribes and are full of errors, misunderstandings, blandishments, and propaganda. You can't take them as accurate predictions of what will happen.

How can this possibly NOT make you think of this:

"I will prepare for long voyages — [I am Savathûn, insidious]
Into the war — [I graffiti this notice for you]
Into the Deep — [These Books are full of lies!]"

It's especially useful to compare the tone and description of events in The Chronicon to it's companion lore book in this expansion, Confessions.

The end of Confessions is especially interesting, in that it positions Calus as a possible in-game avatar of Bungie, or maybe the lore author?

Haha, I would not want to think Calus is my avatar.

I'll have to read the Confessions Book, as I don't think I have it in game yet (well same goes for Chronicon really)

This is not a personal attack, a comment regarding the person, or any type of parallel being drawn
I'm not going to lie, I have had the thought in the past; Could Calus face be an image face-morph of Luke Smith, the Character artist, or someone else at Bungie or Activision?