Aragon joined the Fellowship with full intent of parting before or at Gondor with Boromir. He knew he was going to reclaim the Throne. Aragon as a whole was more badass and more assured of himself in the books. He carried the shards of Narsil and drew the broken sword against the Rinfwraiths on Weathertop, really the first time you see him draw his sword. While spending the 3 months at Rivendell, he goes on patrols with Elronds sons, and Elrond reforfes the Shards of Narsil before the Fellowship leaves Rivendell. A few weeks after they leave Rivendell, the Grey Riders: the group of Rangers from the North who are Aragorns fellow Numenorian descendents as well as Elronds two sons themselves Elf Lord's, set off for Rohan and and meet Aragorn before goring through the ghost way. It's a small band of Men and Elves roughly 30 iirc but more fearsome than the Rohirrim. Aragorn plan is to use the Ghosts to defeat the pirates of the Coast, which they do, and Aragorn releases them for that act then. He and the Grey Riders meanwhile sail the boats up the coast and land at the docks on the day of battle and shift the tide of battle temporarily with just 30 dudes.