Aragorn uses the name Strider when J.R.R. Tolkien first introduces him in The Lord of the Rings.
In The Fellowship of the Ring, Aragorn appears at the Prancing Pony in Bree as a mysterious ranger known locally as Strider. The hobbits initially know him by that name and are uncertain whether he is trustworthy. His weathered appearance and knowledge of the wild contrast with the noble identity eventually revealed.
Aragorn is not merely an adventurer using a random nickname. He is the heir of Isildur and has spent years protecting the northern lands as a ranger. His concealed identity becomes important to the story’s political and historical themes, especially the restoration of the kingdoms of Arnor and Gondor.
Later names connected with him include Elessar, a royal title, and Thorongil, a name used during an earlier period of his life. Those names are not the first identity readers encounter in Bree.