(My avatar sucks, I know it does. Dl But this is as close as I think I can get. If anybody has any suggestions to make it better, though, I'm eager to listen.)
Asbel is a spirited young man with a very strong sense of justice, even more so for that of a knight. He can´t turn away from those in need, and once he has decided on a path it is unlikely that anyone would deter him from it. He may be seen as naive and young (as Malik often states), usually stating ideals considered impossible, such as "saving everyone". After losing someone important seven years prior to the main scenario, he becomes a lot more self aware about his actions and takes responsibility for his own actions.
As depicted in the game, even though he already becomes an adult, he still retains some of his carefree personality from when he was younger, as shown in some of his victory quotes and poses.