Dopamine is an important neurotransmitter, a kind of body chemical which transmits signals between different neurons or nerve cells of the brain. Like many other neurotransmitters, Dopamine is associated with many functions, some of them critical to the normal functioning of the brain and hence the human body.
Dopamine plays an important role in human behavior, cognition, attention, movement, learning and is especially associated with the response of human brain to motivation and reward. It has a huge number of other functions too like stopping the prolactin production, a chemical which is responsible for lactation.
This neurotransmitter has been a subject of study of psychologists for decades. Since it is an important chemical which plays a role in the proper functioning of central nervous system, it has a huge role to play in various eccentricities and myriad behaviors of human.
Dopamine is also associated with addiction of different kinds and other diseases like Attention Deficit Disorder, Parkinson's Disease, Schizophrenia and some other mental disorders which are caused due to the lack of this chemical.
Check out what Psychology Today has to say on Dopamine.