Ray Palmer grew up with an intense interest in science and an analytical mind perfectly suited to it. By the time he hit grad school at a prestigious university his future in academia seemed fairly certain. And then he made an incredible discovery. A chunk of exotic matter that he identified as having originated in the heart of a dwarf star. He went on to study this, and eventually determined that he could create a lens out of the material that, with the proper energy input, was capable of rearranging some very basic properties of matter.
Upon testing his device he found it amazingly effective at shrinking objects and even at changing their effective mass. Unfortunately, use on living materials seemed to inevitably result in destabilization and an explosion.
Not long after this realization, Ray found himself and several other students trapped in a cave during a spelunking expedition He had his device with him, and decided to use it on himself so that he could escape and get help for the others. He fully expected to die as a result. Instead, a latent property in his genetics (the metahuman gene) activated, and rendered him uniquely resistant to the side effects of the machine.
After this incident, Ray made an effort to conceal all his research on the Dwarf Star material, and made himself a suit with more advanced controls so that he could put his creation to use as a superhero. Then he set out, with the same single minded focus that he applies to every other problem, to make himself a better superhero. He trained himself intensely, both physically and in the use of his suit. In addition, he took up Judo, eventually grinning his expertise to mastery of that combat style.
Using his powers for the good of others, and combating various threats large and small (and some large threats that were too physically small for anyone else to handle),
Ray eventually attracted the attention of the Justice League. While he has maintained his civilian identity as a full professor at his university (fortunately his is mostly a research, rather than a teaching, position), Ray has since then been on the "On Call" rolls of the League, and thrown himself into combat when needed.
Molecular Stability: While technically a metahuman, Ray Palmer's inherent power is extremely limited and specific. Unlike other living matter, he does not become unstable and explode when alterning his size and effective mass through the use of the dwarf star matter lens in his suit. This might theoretically profile resistance to some effect that works via a similar process, but it is an extremely specific and limited power whose main effect is rendering his equipment useless to almost any other operator.
Size Alteration: Through the use of a focusing lens created from a fragment of the core of a dwarf star, The Atom can resize matter dramatically, shrinking to an almost unlimited degree. While applying this technology to non-living matter is relatively simple, most living material develops an instability from the process that causes it to explode shortly afterwards. Ray's unique metahuman adaptation allows his system to ignore this effect.
Superhuman Strength and Resilience: By shifting his effective mass into his fists or feet Ray can strike with seemingly superhuman force. In addition, this effect is actually increased at smaller sizes, when his strike can be concentrated into a tiny surface area, like driving a needle into something. In contrast, his tiny size can make it difficult for an opponent to land a hit solid enough do damage him unless he is trapped between two surfaces. (the equivalent of trying to swat a fly in midair).
Mass Shifting: The same device that allows him to alter his size allows the Atom to shift his mass and effective center of gravity. He cannot add mass beyond his normal amount, but he can shift from full mass to atom-equivalent amounts at any size.
Creative transportation: By use of built in thrusters and riding existing air currents, The Atom suit allows Ray to fly. In addition, by shrinking to atomic sizes or smaller, Ray can ride electrical currents through wiring. A favorite tactic in the past was to ride the signal through a telephone call from one end to the other. However, modern systems have made this much less possible because the same trick does not work through fiber optics or over radio broadcast, such as phone signals. Still occasionally useful where hard-line phone systems exist.
Supplementary Systems: Ray has designed addons for the suit for use in fluid environments or corrosive environments and even operation while in hard vacuum, alllowing him to dress appropriately for the mission at hand.
Physics Expertise: Ray has a Ph.D in Physics, and the related technical and mathematical expertise. His specialty has been in the study of exotic matter and its properties and application. He has an extremely solid grounding in scientific principles and methodologies, as well as some practical experience in applied engineering.
Judo: Ray is an expert in this form of martial arts. With its focus on throws and the redirection of momentum, he sees it as an exercise in applied vector dynamics.
Skydiving: Practice riding air currents at small size for locomotion has given Ray the equivalent expertise for maneuvering in freefall conditions of an expert skydiver and particularly in wingsuit operation.
Electronics: Ray's expertise in electronics is sufficient for him to have designed and built the various component systems in his Atom suit.
Atom Suit: The suit he uses when operating as the Atom contains a few highly important features. Most significantly is the Dwarf Star Matter device and the associated controls in the gloves, which allow him to do all the size and mass shifting tricks that compose his powers. He has also set up the suit to miniaturize itself when not in use, and make a transition during the miniaturization process with his normal clothing. This effectively allows him to shrink into the costume when he needs to become The Atom. Besides being made of toubh materials, the unique changes he goes through when shifting sizes make the suit increasingly resistant to chemical and electrical damage as he gets smaller, to the point where he can literally ride an electron flow at his smallest sizes.
Ivy University: As a full professor at a prestigious university, Ray has both a comfortable salary and access to the facilities of the school, including advanced scientific laboratories.
Justice League: An "on call" member of the Justice League, he has historically had access to their facilities and personnel, though he is most frequently called to active duty when a threat demands his particular abilities.
Intellectual. Ray Palmer's personality is largely driven by his intellect. He has a brilliant scientific mind and tends to apply that logical, scientific thinking to all problems. This can be good, resulting in careful analysis and consideration of options and optimum solutions. It can also be bad. It can make him hesitate at a key moment, and it gives him difficulties in dealing with situations that defy logic. Particularly interpersonal relationships (and encounters where magic is involved).
Ethical: While often stymied by personal relationships, Palmer is highly conscious of the ethics of his research and abilities, and of the good he can do for others. He takes up the mantle of a superhero because he feels that he can do real good for people, and will argue strenuously against plans that involve an abuse of power.
Focused: When he has a goal in mind, Ray pursues it with a dedication that borders on obsession, although is overwhelmingly ethical nature does factor in. This kind of hyper focus makes close relationships difficult.
Equipment Dependent: Without the focusing device and its core of nearly irreplaceable dwarf star matter, Ray Palmer is effectively a normal human without any special powers. All the extraordinary things he can do rely on the suit, and damage to it, particularly to the controls in his hands, could render him powerless, or, worse, leave him stuck with his mass or weight shifted until he can affect repairs.
Analytical Mindset: Ray Palmer is first and foremost a scientist. He is used to dealing with equations, empirical data and clear logic. He has difficulty understanding or adjusting when people or circumstances do not match these. Highly emotional or illogical modifications are difficult for him to comprehend, and capabilities that seem to defy science (particularly the use of magic) utterly confound him.
Single minded: When he is focused on a project or a task, it is easy for Ray to become fixated and isolated. Delving into a question of the underlying physics of the universe, whose answer only a handful of scientists could even comprehend, could easily make him lose much of the human contact with the people around him.
Team coordination: The nature of The Atom's powers allow him to face many threats that few other heroes can even access. Unfortunately when this is coupled with the fact that the tech he uses would be fatal for almost any other living being it means that he has to face most of these alone and without support. In addition, without the specialized addons that he sometimes uses for his suit it is extremely difficult for him to communicate with others when he is at micro-sizes.