A Magus is a member of the "Magi Order", which is an interstellar peacekeeping organization of magic wielders.
There has been a belief in magic among the sentients of the galaxy for as long as there have been sentients in the galaxy. The belief in this extradimensional force transcends cultures and species and worlds and with time the great thinkers of the galaxy came to the understanding that every aspect of the galaxy, living or otherwise, is touched by this field in some way. To the sentients of the galaxy, it is something of superstition, it appears to shift their fiction in unpredictable ways, it bends the laws of physics, chemistry and biology. It allows the impossible to happen. Somewhere along the way, sentients realize that this malleable nature of magic goes both ways. It can manipulate their fiction, and they can manipulate it right back.
Those groups throughout the galaxy who began to dedicate themselves to studying the phenomenon of magic and learning how to master it were labeled as witches, wizards, sorcerers and mystics. Some cultures worship magic, others fear it. Through the ages, it has been given countless names: mana, chi, tao, essence, akasa, ethereality, ley lines and thousands of other appellations. No matter how it is named, only one thing matters... magic is real. To those who master it, magic is a powerful weapon, a sure defense and a finely crafted art.
Some of these early magic wielders would revel in their discoveries and live out their lives without passing on their knowledge, others would seek to use their knowledge to obtain riches or power, still others, use it to become respected village shaman, priests of their religions, or leaders of their people. This last group would take on apprentices and teach others how to be aware of magical forces, and how to tap into them and use them for their own purposes. Their knowledge was passed on and incorporated into their culture and religions, where it became encoded into mythologies and cultural behavior.
Eventually the discovery of interstellar travel allowed scientific, religious and philosophical groups to congregate for the first time. The worlds in the galactic community that were aware of the enigmatic mystical powers realized for the first time that they are not alone and the best and brightest philosophers, scholars, priests, and warriors from dozens of worlds collectively started "comparing notes" on what they'd learned. Many were excited to discover common findings about the source of the phenomenon that is called magic. Magic, it was realized, is the common name for the fabulous effects that people are able to create by mentally accessing and controlling certain energies and entities from dimensions tangential to our own. Different skills derived from the manipulation of the extradimensional forces began to spread throughout the magic using community. The revelation of the nature of magic came as a shock to many because various worlds had long since forgotten of magic's true existence and simply regarded it as fantasy. Planets where this had happened include Earth.
After combining all known information, what they realized was that it is because these other dimensions possess physical laws that are tremendously different from our own, the manipulation of the extradimensional forces while in our realm give magic wielders the ability to perform a variety of acts and displays that not only defy the universal laws of physics, but also manipulate and alter many aspects of reality itself on a fundamental level. Simply put, magic is the use of powers from other universes to reshape ours on intrinsic levels. Although compared to the scope of the entire universe, it is within a relatively microscopic and localized area.
After much study, meditation, communion, debate, and experimentation, the groups gathered on Earth to merge and found a new society dedicated to the study of the use of magic. A member of this new society was to be called a Magus, a word that meant "sorcerer" in the ancient Earth language of Latin. This name was chosen by the human delegation of the new group, who were the organizers of the gathering. The collective term for the organization came to be the "Magi Order."
Further research by the Magi revealed that the sentient mind affecting magic works because the brain is nothing more than an organic, biochemical computer. Its functions and operations change with chemical imbalance. It can be affected by outside influences and the environment. Mind affecting magic often targets specific sections of the brain and uses thermal variations, pressure variations, magnetic fields, electromagnetic radiation, electric impulses, sound waves, gravity manipulation and the introduction of foreign biomolecules. A magic wielder, therefore, can use potions, talismans, and spells that incorporate one or a combination of these phenomena to alter the perceptions of the mind, allowing them to summon an extradimensional force to override the usual laws of nature. The incantations of a spell are mathematical in nature, encoded equations of sorts. It's an exotic form of mathematics that is completely incomprehensible to anyone who has not studied magic. Even a simple spell may involve several pages of these complex arcane equations and encoded mathematics. Very powerful and sophisticated spells may fill dozens of pages. The greatest spells known to the galaxy may fill an entire book each.
It also soon became apparent that the "arcane arts" are not an easy path to tread. Few people possess the mental faculties to grasp even the most fundamental arcane concepts. Fewer still could possibly go on to become a successful Magus. For most races only 1 in 10,000 have the necessary genetic traits to become spell casters of any appreciable skill and only 1 in 1,000,000 have the potential to become a truly great Magus. And even then it requires a vast intellect, raw talent, a great deal of patience, endless study, a serious commitment of time, attention to detail and a sufficient teacher. Just a few years after the Magi Order was formed, an edict was issued that declared that they would only accepted those within the 1 in 1,000,000 range to join the Magi.
Over time, the Magi had also discovered that younger beings had an easier time of learning the techniques required to touch and control magic, so they eventually developed a system that actively sought out and identified beings with the correct genetic potential while they were in infancy. With the permission of the parents, the Magi would take children by the first three years of life. These are the most important and dangerous years during development, because at this time, the mental and physical connections in the brain are made. If these connections and thought patterns are already developed, it becomes much harder to re-train the brain and remove undesirable attributes. By approximately ten years of age these characteristics and personalities are firmly set in place. Children that old were often unable to complete the necessary training, and were deemed too wasteful of Magus resources.
Eventually the jumpspace lanes allowed multiple star systems to form the Alliance of Worlds, a wide interstellar government uniting a vast number of diverse species. By the time the Alliance was founded, a natural evolution had taken place within the ranks of the Magi Order. As a society dedicated to research and study, the Magi found it in their best interest to use their abilities to encourage the growth of civilization. In time, the Magi evolved from advocates of civilization to defenders of it. Their society took a more active role in protecting the stability of the Alliance by using magic to aid in peace, justice, and order. When armies of tyranny tried to carve empires of fear and hatred from the civilized systems of the galaxy, the Magi opposed them.
The Magi came to believe that they not only wielded a limitless source of energy, but they also held a social responsibility to wield it in the service of civilization - and to ensure that this power was never abused. Although they suffered their share of setbacks, in time, they became the Alliance's first lines of defense against entities that sought to tear it apart. During this period, the Magi were far less organized than they would later become, but the heart of the Magi Order remained unchanged for the next few decades. Thanks to the Order's efforts, the Alliance expanded and prospered.
This era marks the expansionist age of the Alliance of Worlds. Explorers were still mapping new jumpspace lanes and encountering new species. Colonies became commonplace. Exploration began pushing into new regions of space. During this time, the Magi became the accepted peacekeepers of the galaxy. Individual "Archmages" ran schools where they took in students they deemed worthy and taught with whatever methods they had found most effective. The Magi Order was a loose collection of equals tied together by a sense of respect and camaraderie among different Archmages.
These bonds between Magi were matters of honor and tradition, not law. A fully trained Magi was free to travel whatever path he chose. Not even the most respected Archmage would consider refusing to allow a Magi to undertake a course of action he was set on, even if the Archmage foresaw catastrophe at the end of the path. Similarly, the governments of the Alliance were free to ask individual Magi for aid. Such requests were usually honored, but no law bound the Magi to the Alliance's service. Despite the formal nature of this system, the Magi and the Alliance successfully overcame countless minor threats, working together to unify and protect the galactic government.
A little over half a century after the Magi Order began its humanitarian mission, the Magi reorganized the Order to convince the Alliance of Worlds that they would not become an army of vigilantes. They placed themselves under the supervision of the Alliance's Law Enforcement Directorate, under the Department of Galactic Security. The Order then built a Command Fortress on Mars, the judicial capital of the Alliance.
As the years have passed, the Magi have become the guardians of peace and justice in the galaxy. Legendary throughout the known worlds, they battle interplanetary criminals and settle cosmic disputes. The deeds of the Magi are famous. They are known as scholars, warriors and philosophers. They are all these things – and much more. The Magi have spread across the galaxy, protecting the Alliance and watching over its many systems.