My Solution: came about because one of the supporting characters wore a t-shirt to a picnic. It said "World Docs – Saving the World, One Patient at a Time". I realized that this was the perfect motto for this character and his motivation.
What if every character had a motto, t-shirt or not? That could be a way to distill the character to a phrase – just to remind me who I'm writing and give them a little definition.
So, here's the list of my characters' mottos:
Lani (MC) – I've got to stop people from dieing
Tomas Santos (Dr. and Love Interest): Saving the World, One Patient at a Time
Col. McKittrick – Get it Done
Scotty – Let's Go!
Jerry – How Does This Work?
Walter – In My Day…
Col. Davidson – Let Me Tell You About…
Josie – How are you doing?
Carson – Mine to Protect
Daniel – There more in the world than you've ever dreamed of – and I've turned my back on that part. Don't ask.
Not all of them are t-shirt worthy, but they distill the character and sometimes his/her motivation down to something fairly easy to remember. Scotty is action-oriented. Jerry is an engineer. Etc.
So far, it's working pretty well.