What causes loss of attention and aggression in a child?

It sounds like the symptoms your son is exhibiting are a cause for concern. The first question to ask (in order to determine whether this is his 'personality' or something else) is, are your son's behaviors causing impairment? Are they affecting his school performance, affecting his ability to make and keep friends, or causing problems at home. If so, then they are a problem and should be investigated. In terms of what could be going on, there are a few different possibilities. The first is a behavior disorder, such as oppositional defiant disorder. The second is attention deficit - hyperactivity disorder. Finally, there may be depression or another mood problem. The first step would probably be to talk with your son's pediatrician. Before this appointment, you can help by gathering information. For example, sit down and write out examples of your son's behavior at home. Set up a meeting with his teacher to get evidence for how he is behaving and performing at school. Although thing about whether any recent stresses may be bringing out this behavior (a recent divorce or death in the family for example). Bring all of this information to the meeting you have with his pediatrician, who will be able to direct you towards further steps.