You are a Hellspawn, a being that was formerly human but made a deal with a Lord of Hell for a favor and, in return, were used as an officer for their army. When a Hellspawn is created, their bodies are reforged and infused with a dark energy called Necroplasm. While most Hellspawn tend to look grotesque (and that's being nice), you will look as you currently do, only brought to peak physical condition, bonded with a sentient and constantly evolving neural parasite also made of Necroplasm, which takes the form of a suit linked directly to their host's central nervous system. Yours is a K-7 model, a stronger, more purebred, and adaptive variant, making you a stronger Hellspawn. The suit feeds on the souls of those it kills to enhance, adapt, and evolve itself in response to your needs, wants, desires, and the stimuli it encounters. The suit is able to shift itself into any form you need and can take on various weapon forms for combat, only really limited by your imagination. It feeds off the Necroplasm (or any other spiritual energy you possess) in your body to sustain itself. The suit will move on its own to protect you even when you are unconscious. The costume can also feed off evil energy from the physical world, feeding off the ambient evil of people, animals, and even certain parts of cities.
The combination of a Necroplasm body and Symbiote being much denser than your mortal body gives you greatly superhuman strength that can go toe to toe with high-level angels and demons, speed such that you can dodge light, durability, reflexes, etc.
The greatest ability of a Hellspawn is their vast magical powers, though limited by your power supply, (though this can be replenished with time or absorbing it from spiritual sources). Though the power source is finite, what you can do with it is only limited by your imagination. Some of the ways this magic has been used include resurrecting the dead, firing blasts of necroplasmic energy, teleportation, transmutation, elemental manipulation, shape-shifting, flight, talking to animals, invisibility, multidimensional portals , space-time manipulation, soul manipulation, reality warping, regeneration, feeding off the evil sins and negative energy to augment yourself and refill your reserves, Healing, phasing, psychic powers, telekinesis, cosmic awareness. The list goes on.
Another effect of this transformation is that you now contain 6000 lost souls called the Legion. These are the souls of those who died during the same hour that you were transformed. The power from these souls renders you uncontrollable by the lords of Hell. You can, with practice, learn to access their knowledge and experiences. You can also cause these souls to manifest themselves physically as Hellspawn, allowing them to appear and aid you in combat wherever you are. You can talk to these souls and free them by completing any unfinished business they have, and while this lowers the effective force of the Legion, the souls that choose to stay will become stronger and more tempered to battle, lowering the quantity but raising the quality of the Legion.
Hellspawn are practically immortal unless beheaded by a weapon of heaven or by powerful magic. Though you can be rendered powerless (and therefore mortal) in "Dead Zones" small patches of Earth that are Heaven's domain. Also, you possess a degree of acausality, meaning that any changes to your past or future self will have no effect on the current you.
Note that as time passes, Hellspawn only grow more powerful and dangerous.