Aragorn uses the name Strider when Frodo first meets him in J.R.R. Tolkien’s The Lord of the Rings. He is introduced as a mysterious ranger at the Prancing Pony in Bree.
At that point, Frodo and his companions know little about the man called Strider. Gandalf has arranged for him to help guide the hobbits, but Aragorn’s identity and royal heritage are revealed gradually. He is eventually identified as Aragorn son of Arathorn, heir of Isildur.
Aragorn has several other names, including Elessar and Thorongil. Those names belong to different stages or aspects of his life, which is why Strider is the precise answer for his first meeting with Frodo.