Adeptus Mechanicus.

Mag'ladroth, the Void Dragon. The strongest of the C'tan. Like the others he too was broken into shards. However as the Necron's sleep, the largest of his shards was able to escape. He then flew towards the closest planet with sentiment life to eat there souls. Terra.

The year is 1000 BC. Humanity is no wear near leaving orbit, let alone defending themselves from something so powerful. Luckily they have a defender. The Emporer of Man Kind. He fights and defeats the shard, but he can sense something bad will happen if he destroys it. So he seals it away in the core of Mars instead.

Many years later Mars would be humanitys first colony world. The Emporer wasn't worried since the Void Dragon's shard was **** and he made sure it will remain that way.

Many years after this, the age of Strife began. The pulse of warp energy woke up the Void Dragon shard. Mag'ladroth wispered to the humans of Mars of how the flesh is weakness and how they should become robots, hoping they would 1 day find the Biofurness and feed the C'tan their souls.

The people of Mars developed their own beliefs and became the cult Mechanicus. They worship the Omnissaiah, the machine god. Not aware that he is in the middle of thir planet. They also believe there are souls in every machine called Machine Spirits. If a machine isn't working, that means the spirit inside is angry and must be appeased through muntra and prayers.

After concoring Terra the Empresses of Pleasure came to Mars. She spoke to the Mechanicus and they where convinced she was the Omnissaiah rather then the C'tan in the core of there planet. She has no idea the dragon is awake and is the reason they are like this.

She didn't like that they are trying to become robots but saw that their tech is way better then hers so she pretended to be ok with it.

As the crusade went on the Mechanicus where given colony planets of their own called Forge worlds. These forge worlds are vital to the Imperium as they get most of their wepons, armor and vehicles from them. The Mechanicus keeps the best tech for themselves of course.

Before a machine can be used, they must first perform a ritual on it. This can be ajitating to others that may need the machine emidietly but the Mechanicus don't care.

The Mechanicus don't make new technology, rather they remake old technology and steal tech from the Necron's. However they actually hate the Necron's. Since they know Necron's don't have souls, they also believe they don't have Machine Spirits and believe them abominations. They still think its ok to take there stuff though. Hypocrisy at its finest.

As time go's by, the Empress corrupts them little by little. 10 years into the crusade she convinces them to not replace their genitals with robot parts until the figure out how to turn completely into robots. She also conviced them to have sex and reproduce naturally.

By the time all the Primarks are found, they augment their bodies too look more attractive. Not just for practical reasons.

By 40K they have completely given up on becoming robots. They only become cyborgs to be closer to the machine spirits and too look more attractive. Mechanicus that are not claimed as lover's are the biggest sluts in the Imperium.

There is a large number of Mechanicus that believe the faction has lost their way. Because of this there are allot more Heretek's (Chaos Mechanicus) in this timeline, belieaving Vashtorr is there only way to bring the Mechanicus to their former glory. However there are still more then double the number of loyalist Mechanicusto Heretek's. However, the loyalist Mechanicus is alot less efficient. Yes they are still more efficient then regular humans but they waist alot of time slutting themselves out. At least the Empress gets a big energy boost from them.