This list is for Earth inhabitants only, in which I truly believe that it is accurate. I ask all readers to comment.
Lex Luthor is the most intelligent human being on Earth and one of the most intelligent beings in DC Comics. He has seemingly mastered every science known to the universe. He is able to execute the most effective and efficient solution possible in any given situation. He stands out due to his ability to master any situation, usually against staggering odds.
The Atom, Ray Palmer, is not only a world-renowned physicist but a genius with a Ph.D. He invented a matter-compression technology that allows him to shrink to subatomic levels as he maintained his mass. He also found limitless applications for this technology including gliding on air currents to simulate flight, riding on phone signals for handheld-enabled transportation, and rearranging atoms into Kryptonite in Superman's bloodstream. He is able to produce the most useful, original, and refined solutions to any given problem.
Mr. Terrific is quite the polymath, able to learn complicated skills with ease. He specializes in multiple fields of engineering, medicine, and science. He currently has 14 Ph.D's due to his natural aptitude for learning. He is a self-made multi-millionaire, due to his tremendous intelligence. By six years of age, he not only had learned the theory of time and space continuum but he had read and assimilated the works of Niels Bohr, Albert Einstein, Max Planck, and Richard Feynman. Blindfolded, he also took down both Black Canary and Green Lantern at chess at the same time.
T.O. Morrow is a scientific genius, unmatched in the field of robotics. He is responsible for creating Red Tornado, Red Inferno, and Red Torpedo. He also was the partner of Professor Ivo in building Red Volcano. He also built an artificial soul for Tomorrow Woman, which is incredibly for any human being. He has created incredibly complex schemes and insanely futuristic inventions.
Toyman, Hiro Okamuru, is a teenage genius that has an IQ level of 210. He has been building incredible technologically advanced devices, including a giant Composite Superman-Batman robot since the age of 7. He specializes in biochemistry, cybernetics, genetics, physics, robotics, computer programming, and weapons technology. He is also an expert engineer, able to fix most machinery, robots, and computer programming given enough time.
Professor Ivo is a genius, specifically specializing in cybernetics. He has built Amazo, Amazoid, Composite Superman, and Kid Amazo. He was also the partner of T.O. Morrow in building Red Volcano. He also build the body of Tomorrow Woman. He is insanely intelligent and is the precursor of the android race.
The Brain is a former polymath, criminal mastermind, and is more than capable of plotting out perfect crimes. He is also a master of biology and robotics. He is also incredibly adept at coercion, deceit, and manipulation. He is a genius and is incredibly intelligent.
Blue Beetle, Ted Kord, is a genius, with an IQ level of 192, that has been said to be more intelligent that Batman. Despero once claimed Ted Kord's mind was only second to J'onn J'onzz. He is also proficient in numerous sciences including aircraft, chemistry, engineering, physics, and solar technology. He also had an deep understanding of alien technology.
Doctor Sivana has an incredible intellect, using unique methods to take on Shazam. He is a brilliant inventor, manipulator, and strategist. His gadgets, weapons, and other inventions are matched by no other being. Even though he is quite insane, he is one of the most intelligent "mad scientists" there is.
Batman is brilliant polymath, being one of the most analytical minds on the planet. He gained degrees in biology, chemistry, advanced chemistry, computer science, criminal science, engineering, forensics, physics, and technology by the age of 25. He is also capable of forensic investigation, observation, and inductive/deductive reasoning of the highest caliber. Given any mystery, he can arrive at any conclusions with a fraction of data. He also stands out as the only non-metahuman in the Justice League, being able to stand for himself against incredible odds.
