In The Lord of the Rings film trilogy, Aragorn uses the name Strider while traveling as a ranger.
Strider is Aragorn’s alias when Frodo first meets him at The Prancing Pony in Bree. At that point, Aragorn hides his royal heritage and appears to be a weathered guide who knows the wild roads. His ranger identity reflects years spent protecting the northern lands without openly claiming the throne of Gondor.
The name is not his royal title. Aragorn is also known by names including Elessar and Estel in Tolkien’s wider mythology, but Strider is the name most closely associated with his early appearance in the trilogy. The Hobbits initially distrust him because of his rough appearance and mysterious reputation. Gandalf, however, has already established that Aragorn is a reliable ally and the heir of Isildur’s line.