Patience and tolerance. This is the way.
This unfortunate situation is existing in thousands of cases and it causes lot of sufferings but we should never loose the hope.
There are many wise ways to handle it including:
1. Avoiding any behavior or words which can instigate or trigger his anger.
2. Being cool when he is angry to gradually cool him down.
3. Never be angry reacting to his anger. Your anger will make his anger more.
4. Try to politely explain to him the situation as much is he can understand.
5. Do not involve others unless it becomes out of control, then only those who have effect on him.