In general, kids practice temper tantrums first as a raw emotional reaction, but as they escalate, it's because the child has found that sometimes, tantrums are an effective measure to get what they want. So then the kid resorts to the tantrum again, the results have changed, and they're confused. So they experiment with a bigger tantrum, and they find that this also works at times. They really don't understand the inconsistencies, but it's always worth a try.
And the solution is to eliminate all that uncertainty and take the entire reward system out of play. A tantrum can never result in achieving the desired end. This requires consistency from everyone who is responsible for providing care for him.
Unfortunately, even the "comforting" is, in itself, a form of reward for this behavior.
In the case of my DD, if she wanted something she couldn't have, we'd tell her no, and we'd try to redirect her attention to something else. If she refused to be redirected and threw a fit, we'd tell her no tantrums, to give her an opportunity to get herself in check. And if she continued on from there, she'd find herself in her crib, all the toys and other items removed except for her blankie, until she got her emotions under control. Sometimes that would be pretty quick, and sometimes it took forever, with a few different visits in between. If her behavior continued to escalate, we would warn her of the loss of a privilege, and then the next step was we'd inform her that she'd just lost said privilege. We had to figure out which privileges motivated her, though... after some experimentation we found that taking away bedtime stories worked the most effectively (and still does, six years later). Eventually she'd settle down and we might have a perfectly good day for the rest of the day, but there can't be any idle threats, so once she has been informed that she lost her bedtime stories, she lost her bedtime stories, end of discussion. That might send her into another mini-meltdown at the end of the day, but it also sent a strong message that we mean what we say.
My wife and I were on board with this same plan, and when my wife started taking classes and my mom was watching her in the mornings, we brought her on board, too. Because of the consistency, she got it, and we gradually started dealing with this behavior less and less, until it practically disappeared. The exceptions were when she'd see something inconsistent... my mother-in-law would reward her when she got fussy, and so after visiting with her other grandma, she'd come home and experiment with us again. Then we'd be in the store and she'd see some little kid throwing a tantrum and the parents ignoring it, and she'd wonder why someone wasn't putting that kid on timeout, so she'd experiment with us again. As long as the results stayed consistent, though, the experiments never lasted very long.
We started this when DD was only a few months old, and we never had what people refer to as the "terrible twos." She was a delight to take out into public at that age. Before she was three, she started to develop a talent for negotiation instead, and many times my wife and I were quite pleasantly surprised at the solutions she would propose where we could both get what we wanted.
Of course, it's still an ongoing, daily-adapting process. But the basic theory doesn't change. Just be consistent, and take away the rewards for negative behavior. Because the thing to remember is that every time you have an interaction with a child that young, the child is learning something from it. The question you have to ask yourself every time is, "What did I just teach him?"
This can apply to any negative behavior, not just the tantrums. For instance, the constant re-asking of the same questions:
1) "No."
2) "I said no, and this discussion is over, my answer is final, do not ask again."
3) Warning: "Next time you ask me this, you'll be on timeout."
4) Timeout.