The Markers from Dead Space Explained

The Markers from Dead Space and Dead Space Remake are enigmatic double-helix shaped obelisks of extra-terrestrial origin. Their purpose is to reproduce through intelligent civilizations and create Necromorphs until a Convergence Event is triggered, forming a Brethren Moon.

Two types of Dead Space Markers are known to exist: Black Markers and Red Markers.
Black Markers originate from extra-planetary sources, traveling through space until they impact a suitable planet which harbours life.
After planetfall, the Black Marker would emit a DNA-altering electromagnetic signal which forces the most-intelligent species present to evolve into sentient beings.
Once the beings reach a certain point technologically, the Black Marker will reveal itself by emitting its signal, which will appear to be a source of unlimited energy. It will influence them into creating copies of itself and spread them throughout their territory.
These artificial copies are the Red Markers
Once a Red Marker has been constructed, it will begin to influence the minds of those who made it, making them crazy and violent, and turning the dead into Necromorphs.
In the case of humans, they began to worship the Markers as a sign of God and began a religion called Unitology.
The Marker signal from Dead Space and Dead Space Remake causes depression and a form of dementia in most living beings it comes into contact with. It is believed that the ultimate source of this signal is the Brethren Moons, with the Markers merely rebroadcasting it. Through this signal, the Markers are able to communicate with each other across incredible distances, as it was observed that the Red Markers on Aegis VII, Aspera and Kreemar were able to coordinate and act as one despite being separated by several star systems.

The intensity of this signal depends on the state of the Marker, which displays a sentient ability to control what it transmits and create different effects; however, it is unknown if the artifact itself is sentient or if the intelligence demonstrated is the result of the Brethren Moons speaking through it. When a Marker goes through a state change, the signal will manifest a powerful EMP blast. Additionally, it can be strengthened by the presence of certain catalysts; for example, Marker 2A was able to sharpen its signal after coming into contact with Istvan Sato, whose brain was deemed highly compatible, while Marker 3A was able to strengthen its pulses and relay orders to the Aegis VII Hive Mind through an amplifying pedestal.

In most of those affected, the Markers' dementia manifests itself in the form of hallucinations that drive the victim into a state of paranoia and compel them to carry out homicidal or suicidal actions to prepare for the coming Necromorph infection.
To certain individuals whose DNA is deemed more compatible with the Marker signal, such as in the case of Istvan Sato and Isaac Clarke, the dementia instead reveals codes and blueprints for the creation of Markers, and its hallucinations are more sophisticated, guiding these individuals to perform more complex tasks to further the Markers' agenda. The implantation of a Marker's codes in the minds of suitable hosts is considered a priority to ensure that new Markers are constructed and able to bring about a Convergence Event.
Some individuals would receive different types of knowledge instead of Marker blueprints, like Challus Mercer,
whose contact with the signal gave him knowledge which he used to perform his experiments, and would eventually lead to the creation of The Hunter.

Once enough corpses have been created around the Markers area of influence, the signal begins its next stage, which is the Necromorph contagion. This contagion's genetic code is written in an alien language on the Markers themselves.
The signal reanimates dead bodies, which are then twisted into nightmarish, monstrous creatures that are built for the purpose of killing and infecting other living organisms. This infection occurs not only with the Black Marker, but also where the duplicate Markers have spread.
The resulting creatures are structurally sustained by the Marker's carrier wave, and all of the Necromorphs will fall into an inanimate sludge should the Marker be destroyed, and the signal stop being transmitted.
While the Markers do not directly control the actions of the Necromorphs, which behave as little more than animals with a drive to gather biomass, they can seemingly send out general commands to the creatures through their pulses.
During large-scale outbreaks, the Necromorphs are controlled telepathically by a form known as a Nexus organism or "Hive Mind", which acts as a conduit for the Marker signal, serving as the artifact's second-in-command and answering directly to it.