Three characters in To Kill a Mockingbird represent mockingbirds whose kindness is destroyed by evil:
1) Boo Radley, who is alienated and regarded as evil by his prejudiced neighbors despite being harmless and thoughtful.
2) Tom Robinson, who is wrongly accused of a crime and declared guilty due solely to his race, despite being innocent.
3) Mr. Dolphus Raymond, who is unable to freely express his views for fear of judgment from the hypocritical society in Maycomb.
The mockingbird symbolizes kind-heartedness that is destroyed through interaction with evil, as seen in the prejudice and injustice faced by these three characters in the novel.