Dennis.

Dennis a prodigy, everyone would like to be him in my series, a lot of money, chief of the strongest weapon producer industry, a great influence with 13 assassins under his power and not afraid of what the world will think about him as is public each time that he targets someone for assassination although no one wants to press charges into someone so powerful not even the Government. Since he is the strongest warrior in my series, his power is fearful capable of challenging 3000 enemies when he was a kid before getting adopted by the man that soon with it's heritage made him so powerful in the world's economy. Although he was adopted, he always loved his family even if they didn't share the same blood, for him family was first, everything else was in second category. After finding out where the Ancient dragon's reincarnation is, Aigami the protagonist he begins to send assassins to take everything that Aigami might love, in result to drive him into insanity and awake the dragon inside him dragging the world to it's end periods, but all of this is for his brother... a little kid that never saw the sunlight after a deadly sickness that kept him in coma and the dragon's energy capable of fusion souls back to their bodies and more other things like an elixir is what Dennis needs in order to have what is more important to him than anything... his family.
Edit: by the way he is the main antagonist.

Don't introduce every character in the series and tell us what's their role. That will ruin the series.

lol ok xD

You have presented a lot of information about your character and his setting, but they're all very nonsensical in the way you've presented them. You should take some time to ask yourself some questions about your character and see if the answers are as clear to you as they are to your audience.

= Dennis [is] a prodigy, but what makes him a prodigy? His intellect? His capacity to manufacture weapons? His natural charisma?
= How is Dennis able to publicly assassinate his enemies without any repercussion? Other than his position as the chief of a powerful weapons-production facility, what makes him so influential?
= What...even is his ability that can supposedly stand up to 3,000 opponents?
= What happened to his parents that allowed for him to be adopted by another family? And was his brother adopted by the same family?
= Where did Dennis learn about Aigami's "dragon energy" and how it was able to cure his brother's ailment?

"Also..."

Looking at your Yu-Gi-Oh! picture, I can't help but think Dennis is based off Seto Kaiba, but with an R-Rating that allows him to kill people.
= Intelligent and charismatic orphan who was adopted by the owner of KaibaCorp, whom he later overthrows/succeeds
= Creator and Manufacturer of Dueling Technologies that are used throughout the world as a means of combat (though for a game)
= An egocentric individual who only cares for his younger brother, Mokuba.
= Something about a dragon and the number, 3000. Blue Eyes White Dragon? :^)

xD
Here are the answers:
1- He is a prodigy because his ability to invest money and end up with 10 times what he invested, also his ability with his sword able to cut through bullets.
2- He is influential because even the government fears him, no one wants him as an enemy as he killed 3000 opponent when he was a child and also because of this he is technically the world's leader.
3- In this series there are 5 ancient powers, each one takes up to 30 years to learn and no one could ever reach to such an age to learn them all, but he is technically an artificial human that was born from a project and in it caused such a great explosion that killed all who worked in there. Then his adopted father who is a millionaire adopted him, the reasons were dark but at the same time normal, he wanted a powerful son and one of the founders of the project of artificial humans he hided him from society as his adopted son, but that made no difference on the way that he loved him as family.
4- The third one explain about the parents, now the brother is the biological son of the father years later after the adoption when the father married a common woman.
5- As the most powerful person in the world Dennis has available a great squad of research and information, as they translated ancient scriptures under the ocean and it was written in an unknown language, but with some common patterns etc, they achieved to calculate when exactly the new vessel of the dragon's soul would born. Now the way that he finds out is tanks to the "security" of the planet that has cameras everywhere except private places, as Aigami went possessed by the dragon for the first time and an unknown energy was detected all cameras of that location showed Dennis the dragon holder's identity. Also as the camera looked at Aigami's face his Identification number showed up making possible for Dennis to keep track of every of Aigami's moves.

You should take all of the info you just provided and put at the top of the thread in an organized fashion <3