Betti had good advice about giving him options. Kids do like to have some control over their lives-but keep options limited so that he doesn't get too overwhelmed. Continue being consistent in how you respond to the tantrum and help him find ways to communicate his frustrations without the bad behavior. Also, does he seem to get set on a particular routine? Does he usually get dressed before breakfast? Are his daily activities predictable? It might be helpful to talk him through the morning and make a plan- "first we'll get dressed, then have breakfast. After breakfast we need to get on shoes, and get ready to leave..." etc. If he knows what is coming next, he might be less likely to have a meltdown.
Regardless- you really should talk with a pediatrician for advice-if that doesn't seem to help, a child psychologist would be a good option. There are a number of things that could be affecting his functioning. A doctor should be able to give you more information if you give them lots of detail about his mood and the kinds of things that cause him to have a meltdown.
Good luck! Just keep remembering all those smiling times.