This is my opinion, I haven't finished Dawn of the Clans, A Vision of Shadows, or The Broken Code yet so that is why deaths from those book aren't on this list yet.

1. Yellowfang: I cried like a baby when she died, like it was so sad, she went back to save another cat (Forget who now), but she sadly died from smoke inhalation, like her last few words with Firestar were so sad, she died a hero. 

2. Firestar and Bluestar: Both died heroes, Firestar died protecting his clan, like a true hero, we had him since the first series, and he dies on us in the 4th series. Sure he's in Starclan, but it's not the same as having him alive. Bluestar, omg this was sad, she died saving Firestar and her clans from dogs. Then her final goodbyes to her kits and Firestar is the part that had me crying. Like I salute you both Firestar and Bluestar, respect!!!

3. Tallstar: I knew he was gonna die eventually, but it was sad that he died reaching their new home. Like I cried. My favorite character, decides to go bye-bye on me. Like Tallstar that is unacceptable that you died on me! 

4. Hollyleaf: She died for her clan as well, she was a hero, saved her clan from an attack through the tunnels, saved her clan when the dark forest attacked, she died a hero. 

5. Lionheart: Sure he was only in book 1 of the first series, but it was sad as heck for me.

6. Sandstorm: I cried, I actually cried. Like Sandstorm was awesome.

7. Onestar: Unpopular opinion? Yeah I hated him for awhile, but when he died saving all the clans from Darktail. Like he sacrificed himself, and I feel like deep down he was a good cat.

8. Sandgorse: Tallstar's father, I didn't like him, but it was sad when he died, like it seriously hurt Tallstar and that's why it was sad for me.

9. Crookedstar: I loved Crookedstar, he has a tough life, but didn't let that get in his way.

10. Shrewclaw and Badgerfang: Shrewclaw died fighting for his clan like a true warrior. Badgerfang died too young, like damn his final words with his mentor was hella sad.