The Old One Empire builds Loki to quench its thirst for blood

Scientific achievement

Fun fact: the dates on these mean nothing except the order of events. Unless it's actually in the later stages like when humanity is strutting around in space and exact dates are necessary due to the many events being more crammed together, it's probably just a number put their for estimation and it doesn't matter that much anyway since the general gist is "plants weren't even on land yet at this point".

Having processed the alien cult into edibles and made countless subspecies of themselves to survive on other planets, the Old Ones found themselves having quite the taste for the blood of xeno scum and enforcing an ideology in relation to anything they believed to pose a potential threat to the Old Ones that went a little like this:

"Hippitty hoppitty your heart will now stoppitty."

Loki was a means to this stoppitty end.

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Loki was built as a giant habitat for the Old Ones, who at this point somehow knew how to convert matter into exotic matter and back into regular matter and utilised this when building Loki to make it as ridiculously big as possible.

More important than the giant planet being built was its facilities that included the portal makers. These portal makers would make portals from within these facilities to planets that met some of the conditions for being habitable, which the Old Ones knew of through good ol' telescopes on satellites, and then the Old Ones would go in to make it less habitable. Questions such as "why not just colonise those worlds?" and "are these Old Ones going too far" can be answered with: "they're not naturally a very inventive species", "they were extremely xenophobic", "they didn't want to overstretch their empire and risk creating a rival one of the same species" and whatever other nonsense I can call forth from my buttocks later.

Anyway, about building this Loki (which was not its name at the time): it was a giant, hollow sphere with several thousands of miles deep of crust followed by a lot of air in the middle followed by vacuum followed by an exotic matter core pushing out at everything to prevent the thing's gravity from collapsing in on itself. Massive cities were built in this crust (where gravity was often wonky), under this crust (where gravity was reversed) and on top of this crust where the sun DID shine (where gravity was normal). Countless Old Ones of the original genotype of Old Ones, which got special rights, settled here and soon the entire planet was another Old One urbanised mess.

Now the effects of this thing: the Old Ones using it meant that they were able to prevent the formation of life on countless planets and completely wipe out life on others. They massacred countless space empires from existence and stole their technology, making them stronger as a species despite their near inability to invent their own stuff as a result of having next to 0 in imagination and creativity points (although this is probably part of why they stuck around so long; they never really used technology in especially weird ways due to their inability to come up with said weird ways of using tech, causing them to never get around to things like having to take on robot rebellions due to a lack of robots. Pretty much all their tech either came about by accident or was stolen).

This also laid the groundwork for modern life in the galaxy being so Earth-like as it effectively wiped the slate clean of everything else and so when the Old Ones went while leaving Loki behind, it made it possible for life that could be evolutionarily traced back to Earth to spread across many locations in the galaxy, especially since an AI kept making these portals to habitable planets of type 1: potential for Earth-like life to survive.