Deadpool Wiki

Deadpool,old name Wade T. Wilson who was a common person and worked as a government agent.He joined Weapon X Plan because of his cancer and he hoped to have the self-healing ability of Wolverine to get rid of cancer.
He got the this self-healing ability from the Weapon X Plan and was injected the special DNA but this operation made him lose his face look.Because of that Wade can not control his emotion and mood.Weapon X Plan listed him a “failure product” and put him in a prison to research and torture him.

The name Deadpool came from then.It was said that there was a game named “dead pool”that shows whom would be tortured to die next.But,because of his self-healing ability,Wade did not die.When he was dying,he saw the Death and fall into her and so Wade kept trying to kill himself to meet the Death and due to the self-healing ability he failed a lot of times.
So he felt despair and killed the guards and ran away with other “failure products”.Later he came a “hire shoulder”.
Later Thanos knew Deadpool love his beloved Death and so he did a magic on him and so Deadpool can not die forever which means that he can not see the Death forever.So Deadpool became more powerful and so he became a super killer.Because he was working as an agent and so he is a good at all kinds of weapons.He had a Teleport device on his waist,as it did not work right frequently and so he always made funny things.

Because of the special DNA in his body his cognitive ability and memory are losing.Although Deadpool is very ugly,he is romantic.
Later Deadpool movies appeared and many game company produced a lot of Deadpool computer games.

Fro wiki:

A dead pool, also known as a death pool, death watch, dead cert or ghoul pool, is a game of prediction which involves guessing when someone will die. Sometimes it is a bet where money is involved. The combination of dead or death, and betting pool, refers to such a gambling arrangeme.An example of the concept is where a list of celebrities is decided upon, and the names are placed into individual sealed envelopes. Each player picks a sealed envelope and writes their name on the outside of it. Each week, each player pays a small amount of money. When one of the celebrities on the list dies, the envelopes are handed out and opened, the player who has the envelope with the name of the dead celebrity wins all of the accumulated cash.

source: http://rainworld.info/category/deadpool-costume/