Timeline

Overview
The timeline can be divided into 4 approximate segments:

Pre-Betrayal - Before the point at which Providence trapped Mithrix on the moon.

Post-Betrayal - After the point at which Providence trapped Mithrix on the moon.

Before Present - Before the events of the game take place. Unknown if they happened before or after the Betrayal.

Present - During the events of Risk of Rain 1 and Risk of Rain 2.

Pre-Betrayal

 * Mithrix and Providence (the brothers) somehow exist on Petrichor V, be it born or not.
 * The brothers chase glass frogs in the sun.
 * Providence catches Mithrix tossing worms into a gravity well.

- A few millennia pass from this point to the next -


 * The brothers create teleporters, which they call "gates."
 * Mithrix learns that he loves design, while Providence learns to create and shape.
 * Mithrix builds Bulwark's Ambry, as a place for Providence to create anything he wants using the 4 elements of the universe Mithrix found. In the Ambry, Providence creates the artifacts.
 * The brothers, as they reshape the planet to their liking, talk about Sundered Grove. Mithrix loves triangles, while Providence loves circles and rings. They both love trees, though.
 * The brothers start to create golems, which they call "Guardians."
 * Aurelionite is created, and Mithrix has to seal it away, as it is sentient and dangerous to him and Providence. This is because Providence added more soul than Aurelionite's design required, making it both powerful and unstable.
 * Mithrix shows Providence how to create a golem with no soul, being the original design of the Lunar Chimera Golem. Later, Providence would adapt this design when creating the Temple Guards.
 * Much time passed before "She" came. It is unknown who "She" is, but it is known that she is no female that is known in Risk of Rain.
 * The brothers know that "She" is coming again soon, and Mithrix wants to show her some of the gates they've made.
 * Mithrix creates the first and only teleporter that can travel between planets, which is known to be the Primordial Teleporter. He does this because he wants to find more of their own species and leave behind Petrichor V, which has doomed species on it.
 * Providence, who cares for the beings on Petrichor V but knows his brother does not, allows Mithrix to go to the moon. Once Mithrix is there, Providence locks the way back and traps Mithrix on the moon. We refer to this point as the Point of Betrayal.

Post-Betrayal

 * Providence gathers monsters from other planets and brings them to Petrichor V.
 * The Elder Lemurians create the Temple of the Elders as thanks to Providence, whom they call their "Hero."
 * The Imps invade from the Red Plane, trying to retrieve an unknown artifact, but become trapped on Petrichor V due to Providence's physical presence. Some of them attempt to overpower him, but fail.
 * The ancestors of the Grovetenders create the Scorched Acres as thanks to Providence, who saved them from death. Providence does not seem to notice their efforts to honor him, so the generations of Grovetenders and their wisps endlessly tend to the Scorched Acres in hopes of repaying him someday.
 * Creatures from the Void arrive at Petrichor V in an attempt to capture it, but are foiled various times by Providence, making it "the one planet they couldn't take".
 * "She" had came and died, giving her blessing to Providence. What the blessing was is unknown, but her sacrifice is unknown to the inhabitants of the planet. Mithrix resents that Providence was given her gift.
 * Mithrix begins creating lunar items with help from others on the moon. He scatters the items across Petrichor V, as any being that finds them is corrupted by his influence and becomes his servant.
 * Mithrix tells his servants (primarily the Twisted Scavengers) to go to the monolith in A Moment, Fractured, and to activate it while holding his beads. It sends them to A Moment, Whole, a place where they can find peace, safe from the coming tidal wave of his vengeance.
 * Providence, to try and stop his brother, hunts down any that find lunar items. Any and all such items he finds are thrown into Cleansing Pools and turned into Pearls, effectively destroying them.
 * Mithrix designs and builds the Lunar Chimera Wisp (inspired by the Greater Wisps and Clay Templars) and the Lunar Chimera Exploder.
 * Mithrix details his plans for getting back at his brother who betrayed him, noticing Earth and planning on destroying it by building a Grander Teleporter to get there, all to see the look on Providence's face.

Before Present

 * The War of 2019 takes place, otherwise known as the War of Slopes. It is stated to be the bloodiest conflict in human history. Artifacts such as the Berzerker's Pauldron and War Horn are retrieved from the site of the battle.
 * The High Court becomes the most technologically advanced society known to humankind, keeping their advancements a close secret. The House Beyond travels deeper into space than the rest of the Court.
 * An Artificer of the High Court somehow is trapped by the Newt in the Bazaar Between Time.
 * Fireworks are re-legalized for residential use in 2054, having been banned previously after terrorists disguised missiles as fireworks.
 * The Followers of N'kuhana grow in popularity, a cult that is fully devoted to Her Concepts. In one particular instance, a ritual sacrifice by them is stopped by a boy who attempted to save his sister. The dagger they used ends up on the UES Contact Light.

Present

 * The UES Contact Light goes off its scheduled course to take a detour through an unknown star system. The detour was requested by an unknown individual, redacted from the blackbox data.
 * On day 5 of their detour, the UES Contact Light discovers Petrichor V and begins studying the planet. Coordinates are marked, and xenoarchaeologists and engineers are sent down to the surface.
 * After exploring Petrichor V for roughly 35 minutes, the xenoarchaelogists and engineers discover a teleporter. Hoping to find a matching pair, they load the collected teleporter into the cargo bay. It is unknown how they brought it aboard.
 * About 25 minutes after the teleporter is loaded, Providence arrives onboard through it, wreaking havoc aboard the ship and causing it to crash in the span of 4 hours.
 * At some point during those 4 hours, Kur-skan the Heretic appears on the ship via a blue portal, rushing to the front to repair the ship so it can fly, so she would be able to escape. As she reaches the bridge, Providence appears behind her and kills her instantly.
 * The ship spills its contents across the entire planet and into space around it, with some remaining in its cargo bays. Any survivors evacuate the ship via escape pods to the planet below. Only 56% of the escape pods are launched before Providence presumably kills the rest of the crew aboard.
 * Of the pods that escaped the ship, one contains the Commando from the first game, also known as The Survivor. The rest of the pods contain the surviving crew of the Contact Light, who establish rallypoints for survival and reconnaissance such as Rallypoint Delta.
 * The Survivor, in the span of a few weeks, travels through the teleporters to reach the remains of the Contact Light. He documents his time on the planet via monster logs and some item logs, the items he found being classified as field-found. Along the way, he frees Acrid from its cage in the Sunken Tomb.
 * The Survivor battles and kills Providence, and uses the still-functional components of the Contact Light to escape the planet. The Survivor is also the only survivor to escape. Acrid, instead of escaping, is captured at some point by the Void Reavers and detained in the Void Fields.
 * With Providence dead, the creatures of the Void move to capture Petrichor V, causing in-fighting amongst monsters as some are controlled by Void Infestors.
 * The survivors Marion, Pugh, Larsen, Dillon, Carney, Stevens, and Hitchcock end up in the Wetland Aspect. Hitchcock is killed by Stone Golems. To escape the Golems, Marion gives the dagger she had in her backpack to an unnamed survivor, who kills her with it and manages to stop the Golems with its power. Carney later discovers a book in a chest nearby called the N'tormat, which describes N'kuhana's cult. The unnamed survivor becomes corrupted by N'kuhana's influence and murders the other survivors, sacrificing Carney to the altar they built in the cliffs below.
 * The rest of the survivors die out over time, meeting grisly fates all across the planet. Acrid survives its imprisonment in the Void Fields, setting it up to return for the events of the second game. It is the only survivor to appear in both games.

- An unknown period of time later -


 * UES [Redacted] responds to the distress call of the Contact Light. The ship is well-equipped, with units designed for exploration, science, hydroponics, and more.
 * Members of the UES [R] go across the planet to explore, document monsters, environments, retrieve Security Chests of the Contact Light, and other things.
 * Some scientists on UES [R] find the Artifact Teleporter on Sky Meadows, leading to the Bulwark's Ambry, and successfully manage to connect to it using their technology.
 * Other scientists dissect monster parts, while exploration groups bring in artifacts and materials from the planet to study.
 * During their time around the planet, REX breaks protocol and becomes sentient. The head of the Hydroponics division tells the hydroponics team to terminate it due to the dangers it poses. They do so, and REX ends up in the Abyssal Depths, out of fuel.
 * It is entirely unknown whether the crew of the UES [R] went back to where they came, or died on the planet.

- An unknown amount of time later -


 * UESC re-hires a famous retired Captain, who worked on many secret projects for them before, for one last mission. He agrees, but is suspicious of the pretense of it being a "rescue mission," since he is assigned the UES Safe Travels (which is not a rescue ship). As a precaution, he requests that the ship be stocked with armaments and supplies.
 * Various mercenaries are sought out and hired for the expedition, including bounty hunters such as Huntress, and Commando who is reassigned from active duty.
 * Before the UES Safe Travels takes off, the Bandit sneaks onboard, taking advantage of everyone wearing environment suits and being hired mercenaries.
 * Hiroshi and Rico, maintenance crew and part of UESC, kill time by modifying a MUL-T unit inside of a hangar and enabling its learning module. They fail to call the MUL-T back to disable the learning module.
 * The Safe Travels arrives in orbit of Petrichor V, getting the distress signal the Contact Light sent out during its crash. The signal details monsters attacking the ship. The Captain decides to send the crew down anyway, both in drop pods and drop ships.
 * During the first 24 hours, major casualties are sustained, with many of the ships being crashed and destroyed. An unknown amount of survivors make their way through the teleporters on the planet, eventually reaching the moon.
 * Once on the moon, the survivor(s) discover a rescue shuttle that has been captured by Mithrix and placed under a force field, with evidence of a struggle having taken place as a number of dead Commandos can be found around it.
 * The survivor(s) battle and kill Mithrix, freeing the rescue shuttle. The Void Reavers, just after Mithrix's death, invade the moon and begin an attempt to capture it.
 * The survivor(s) escape in the rescue shuttle, just before the Void Reavers fully pull the moon into the Void Fields.