Much has been said about developing three-dimensional characters and how incorporating the senses can breath life into them. Most authors are comfortable with having their characters feel love, hate, fear, and even desire. However, one of the most powerful and often most motivating emotions is grief. After all, desperation is a common reaction to denial, anger, or bargaining, three of the five stages of grief. It is perhaps one of the most underutilized emotions in writers' tool boxes. This may be because writers feel no one wants to read depressing narrative or connect with a sad, deflated character.
If that's the case, it's not necessary to make the main character experience grief. A bad guy who acts in despicable or desperate ways could have grief as a believable motivation. Recall any recent bad guys who were desperate to reanimate a dead spouse, no matter the cost? Batman comes to mind. Then there's The Mummy and Dracula, just to name a few.
And who says the main character can't experience grief without being a sad sack? Can't they pull themselves up and accept the death (final stage of grief that many never reach at all), getting on with their lives for the sake of their kids, parents, friends, employees, etc.. That makes them empathetic and makes the reader want them to be rewarded for their selfless sacrifice and their undeserved suffering.
I want to also address characterization and how a main character's reaction to grief can be manipulated to push the plot. To say that a character must remain "in character" while reacting to grief is misleading. Coping with loss is a personal and singular experience. No one can understand all the emotions a mourning individual is experiencing and no one goes through the cycle smoothly or in a linear sequence. This is very useful for a writer because a character can act or do things that are "out" of character, due to grief. Their behavior is also going to be modified by who it is they are mourning. One mourns differently for a child, a parent, a friend, or a spouse.
Finally, its important to remember that characters don't just grieve for people. They can also grieve for a pet, a career, or anything else they value or cherish and lose. Losing a fortune would do it for most of us. So don't be afraid to pump up the drama and raise the stakes straight over the heart.