5 – Jinbe
While initially assisting Luffy only to protect and rescue Ace, Jinbe grew so fond of Luffy that he proclaimed while fighting Akainu at Marineford that he would gladly lay down his life to protect Luffy. It was Jinbe who also brought Luffy out of his self-pity and doubt. The fishman made Luffy realize that even though Ace had died, he still had his own pirate crew. After the battle of Fishman Island, in which Luffy lost a large amount of blood, Jinbe offered his blood for the transfusion.
4 – Monkey D. Dragon
Their only meeting was when Dragon rescued Luffy from being captured by Smoker in Loguetown.
3 – Mr. 2 Bon Kurei
Luffy became good friends with Bentham after he apologized for causing them trouble in Alabasta, and distracted the Marines so the Straw Hats could escape. Bon Kurei went as far as to give his life away to save Luffy and other Impel Down prisoners by posing as Magellan and ordering the opening of the Gates of Justice during the Impel Down Arc.
2 – Shanks
Shanks is the pirate who saved Luffy’s life twelve years ago in his hometown. He sacrificed his arm in order to save Luffy from the Sea King.
Shanks said he bet his arm for the future. He probably did this intentionally to show Luffy what it takes to become a pirate. Luffy had stated to him at a young age he wanted to be a pirate as great as Shanks and Shanks wanted to show him what it means to be a pirate and that means risking everything and possibly losing your arm or worse your life.
1 – Portgas D. Ace
Hunted by the World Government for his lineage, Ace was captured and sentenced to death, which resulted in the Battle of Marineford in an all out clash of powers. Ace was freed, but he sacrificed his life to protect his younger brother Luffy from Akainu.