ELFANGOR
Prince Elfangor was the one who gave the Animorphs their morphing power. His full name if Elfangor-Sirinial-Shamtul and he is the brother of Aximili-Esgarrouth-Isthill and the father of Tobias (explain later).
After landing on Earth and giving then Animorphs their power he urged them to hide, although they didn't want to, as Visser 3 was coming and he knew he would be killed. He was right. Visser 3 morphed some horrible outer space monster and ate Elfangor.
But this was not Elfangor's first time on earth. Elfangor had actually come to earth to find the Time Matrix which he had buried on Earth many years before. Once he reached Earth he found that he was to weak to find it so instead he had given the five youths the morphing power hoping that they would be able to defeat the Yeerks. He also knew Tobias' name and knew that Tobias was his son.
Many years before after a very bad fight, his friend had been trapped as a Taxxon and his prince had become the first and only Andalite-controller. Elfangor ran away to Earth with a human that he had rescued from another alien species.
Once on Earth he morphed a human, a mixture of DNA from various people. His name became Alan Fangor and Loren had told him most humans shortened name so he would be called Al Fangor. He married Loren (the human that he rescued), went to college and began working. His life was very happy and although he missed the battles and the whipping of his tail sometimes, he was happy with his decision.
Then one day he returned home after work to find that Loren had gone to the doctor and some strange old man was in his house. After a short conversation he discovered that it was the Ellimist. He said that Elfangor had messed up time and restored his Andalite body and sent him into a battle. Just before he went he discovered that Loren was pregnant and he decided that he wanted to return to Loren but the Ellimist said that was not possible and that the boy would be raised as someone else's child and that Loren's memory would be wiped of him.
Elfangor survived the battle and afterwards became a hero. He was in many more battles and he also began to teach his younger brother how to battle and things like that.
When he died, the Animorphs considered he was a true hero, as he died so that the Animorphs would live and be able to protect their world. Elfangor also had a dome ship named after him, which in Andalite customs is about the highest honour ever.
For Elfangor's full story read, The Andalite Chronicles.