The blood elves (or sin'dorei, "children of the blood" in Thalassian — pronounced [ˈsiːndɔraɪ], [siːnˈdɔraɪ] or [siːndɔreɪ]) are high elves who changed their name after the Scourge invasion of Quel'Thalas. Their new name is a dirge, referencing both the blood of their many brethren who fell during the Third War, and their royal lineage.
For nearly 7,000 years, high elven society centered on the sacred Sunwell, a magical fount that was created using a vial of pure arcane energy from the first Well of Eternity. Nourished and strengthened by the Sunwell’s potent energies, the high elves’ enchanted kingdom of Quel'Thalas prospered within the verdant forests north of Lordaeron. During the Third War, however, the high elves were nearly scoured from Azeroth. Led by the death knight Arthas, a Scourge army stormed into Quel'Thalas, slaughtering almost ninety percent of the kingdom’s population. Arthas then used the mystical Sunwell to resurrect the fallen necromancer Kel'Thuzad, irrevocably tainting the fount in the process. Prince Kael'thas Sunstrider rushed to his homeland's aid, and the survivors of the onslaught were renamed the "blood elves" in honor of their fallen people. The tainted Sunwell was destroyed, but the elves had grown addicted to its energies over the years, and were left weakened and despondent without them. Kael'thas assured his brethren that he would find them a cure, and left Quel'Thalas in the hands of his regent, Lor'themar Theron, while he traveled to avenge his people and find a way to sate their hunger for magic.