Sitting beside Juror #8, Juror #9 shows us throughout this movie that he's a strong believer in justice and sympathy. The first thing we notice about him, though, is that he's much older than the other jurors—probably somewhere in his eighties. But he surprises us when he stands up to Juror #10's racist comments and says, "Do you think you were born with a monopoly on the truth? Certain things should be pointed out to this man."
This act shows us that #9 is a guy with progressive ideas—and it also shows that he's not afraid to stand up to bullies.
Our respect for Juror #9 only grows when he becomes the first person other than Juror #8 to give a vote for Not Guilty in the murder case. He makes this clear when Juror #3 accuses #5 of changing his vote, and #9 says, "He didn't change his vote. I did." When asked to explain why, he says, "This gentleman chose to stand alone against us. That's his right. It takes a great deal of courage to stand alone even if you believe in something very strongly. He left the verdict up to us. He gambled for support and I gave it to him. I want to hear more. The vote is ten to two."
So there you have it: Juror #9 is like the second-in-command when it comes to justice and sympathy. He might not be as young or smart as Juror #8, but his heart is just as good.
Even after we've come to respect him, Juror #9 shows us just how strong his sympathy is when he explains to the other jurors about why an elderly witness in the murder case might have made up his testimony. He backs up his theory by saying, "I think I know this man better than anyone here. This is a quiet, frightened, insignificant old man who... who has been nothing all his life."
Since he can identify with being old and forgotten, Juror #9 concludes his big sympathy speech by saying, "Gentlemen, that's a very sad thing—to mean nothing. A man like this needs to be quoted, to be listened to." So in this case, he's shown us how sympathetic he can be and how convincing he can be: he actually ends up making some of the other jurors think that the elderly witness has made up parts of his testimony.