Part of the fun of writing a series is having the chance to turn the spotlight on secondary characters. That’s also part of the challenge.
I have a tendency to write stoic heroes who are bound by duty and honor. I also tend to give those heroes friends and brothers who are a little flip and irreverent. These sidekicks do a good job of pricking the ego of the hero, humanizing him. But when it’s the buddy’s turn to take center stage, it becomes my job to torture him. That’s where the problem lies.
You have to make your characters suffer or they won’t change and grow. The trick is to make a secondary character who was a joker mature without losing his personality. He can have a dark, or self-deprecating sense of humor, but when he’s really suffering the reader needs to feel it. You have to make the hero’s pain real and profound for his eventual triumph to be meaningful. Humor can still work in these situations. The character may try to deflect his pain with humor, or he can turn sarcastic and biting. But however he reacts, he can’t be quipping as usual.
I faced this problem when I wrote Ragni in as the hero of FORBIDDEN TALENTS. 
He had to become more serious given what I was putting him through, without losing the essence of what had made him appealing in DANGEROUS TALENTS. One technique I employed was keeping the hero from the earlier book, Dahleven, around. By comparison with his older and more serious brother, Ragni is still irreverent. By the end of FORBIDDEN TALENTS he’s gained a bit more gravitas, even if he’s still more than ready to give Dahleven a hard time.
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FORBIDDEN TALENTS is FREE from Kindle through Tuesday, 10/16/12.
Frankie's Soapbox 
That is so totally true Frankie. I have a similar situation with two sequels I’ve been working on. Let me tell you, it’s been slow going. In fact, I wrote a whole other novel this summer while avoiding their books! Glad I’m not the only one whose faced the secondary character turned hero struggle!
Pretty soon I’ll be starting work on GUARDIAN, the sequel to LIGHTBRINGER. That’s Gideon’s story. (I obviously wasn’t thinking when I named him Gideon the Guardian!) His story is going to be a real challenge! Lucky for me I have some other work that I can use to postpone starting on it.