Evil Marker
King
Loyal to an Elven Family.
In high reaches they sing.
Thorondor
Thorondor, the Lord of the Eagles, was the greatest of the Eagles of Manwë king of the Valar.
Answer: Thorondor, King of the Eagles in the First Age, made his nest in the high mountains, and clawed Morgoth, scarring ("marking") his (evil) face. I wouldn't call Thorondor "loyal" to anyone but Manwe (and the other Eagles); but he rescued various High-Elves on a few occasions, and his eagles kept watch over Gondolin.
(confirmed correct 1/2020)
NOTE: Bobbins had the answer incorrectly spelled as Thorondir.
Tolkien Gateway: Thorondor