Aragorn uses the alias Strider when he first appears in J.R.R. Tolkien’s The Lord of the Rings.
The hobbits meet him at the Prancing Pony inn in Bree, where he is introduced as a mysterious Ranger. Strider protects the travelers and guides them away from danger, but his identity and royal heritage are initially hidden from them. The name reflects his life as a wandering Ranger of the North.
As the story develops, Aragorn is revealed as the heir of Isildur and a descendant of the kings of Gondor and Arnor. He later takes the royal name Elessar and becomes king after Sauron’s defeat. Strider therefore describes only one stage of his identity.
Elessar is not the alias used at his first appearance, and Thorongil is another name Aragorn used earlier in his life. Halbarad is a separate Ranger and relative, not Aragorn himself.