Rabonim
Rav Meir of Rothenberg.
Captured and held for ransom by an evil king, he refused to let himself be redeemed because he was concerned that others would then be captured and held for ransom. He died in prison after several years.
Rav Aharon Kotler.
The existence of the thriving frum community of Lakewood, NJ and its huge bais medrash where thousands upon thousands learned are solely due to his establishing the yeshiva there.
Relatives
Jewish
Eli Cohen, who lived for years in deep cover, rising in rank within Syrian society and government, all the while spying for Israel and proving valuable information that saved lives in the Six-Day-War. He knew that discovery meant certain death, and he endured extended periods away from his family. He was captured when Syria traced his radio signal, and subsequently hanged.
Chaim Smadar, a security guard who willingly sacrificed his own life to save a supermarket full of people. He could have saved himself, but instead grabbed and held a suicide bomber before she could enter the store, telling her “You are not coming in here. You and I will blow up here.”
Secular
Pat Tillman, a professional football player, turned down millions of dollars that he would have made as a professional athlete to enlist in the army and fight for his country. He became a member of the elite Army Rangers, and later died in the line of duty in Afghanistan due to friendly fire.
(the above is just a small sample)