Théoden (Bernard Hill) is an intriguing character in Lord of the Rings. He is the King of Rohan and uncle to Éomer (Karl Urban) and Éowyn (Miranda Otto), who are both compelling protagonists as well. After the demise of their parents, one of whom was Théoden's sister, Théodwyn, Théoden adopted his nephew and niece and raised them. After the passing of Théoden's son Théodred, Éomer became his heir. However, there was trouble brewing in Rohan.
Théoden grew old and weak and began to listen to the advice of Gríma Wormtongue (Brad Dourif). Grima, of course, really worked for Saruman (Sir Christopher Lee) and was there to mess with Théoden. He made sure that his real master, and therefore Sauron as well, was happy. And it is with his advice that Théoden agrees to lock up his nephew and heir, Éomer. It is then that Gandalf (Sir Ian McKellen), Aragorn (Viggo Mortensen), Legolas (Orlando Bloom), and Gimli (John Rhys-Davies) arrive in Rohan.
Gandalf advises Théoden to resist Saruman, but Théoden initially doesn't listen. Luckily, everything eventually works out for Gandalf and the rest of the Fellowship members. Théoden shakes off Grima's and Saruman's control and orders Éomer's release. Gandalf then advises Théoden to fight against Saruman and his armies. Théoden and his people, along with Aragorn, Legolas, and Gimli, head to Helm's Deep, where a battle takes place between the people of Rohan and Saruman's forces. The Elves of Lothlórien are also present for the battle in the movie version, honoring the alliance between Men and Elves. Théoden and the rest of those at Helm's Deep continue to fight. Théoden eventually loses some hope, but nevertheless, he rides out with Aragorn to attack the enemy. Gandalf and Éomer then arrive with reinforcements. After the battle, Théoden goes to Isengard with Gandalf and meets Merry (Dominic Monaghan) and Pippin (Billy Boyd).
Théoden leads his people in the Battle of the Pelennor Fields, against Sauron's forces. He fights the Witch-King but is seriously wounded. Éowyn then fights to defend her uncle, and along with Merry, is responsible for the Witch-King's demise. Théoden sadly perishes from his wounds. This is what actually happens in the Lord of the Rings books and movies, but let's imagine an alternate version. Let's say that Gandalf was for some reason or other not present when the Fellowship members arrived in Rohan. Would Théoden have been able to shake off Grima's and Saruman's control? Or would he have remained in his weakened state? If he had remained weaker, would it have affected the War of the Ring? Without his help, would the fight against Sauron and his allies have been effective?
Without Théoden and his people, the outcome of several battles would likely be different. The Battle at Helm's Deep wouldn't have happened at all, and therefore Saruman would have had a lot more forces to send Sauron. The Battle of the Pelennor Fields would have also probably had a different outcome. Without Théoden's presence, the Witch-King wouldn't have been weakened. Éowyn also wouldn't have been there, leaving Merry to face the Witch-King alone. Could he have defeated the Witch-King by himself? Or would Sauron have kept his greatest and most fearsome general? Would the War of the Ring have been doomed without Théoden's help? Possibly not, yet it seems that Théoden and his people play a critical role in some battles. And without their presence, the battles likely would've been harder to win.
So would the War of the Ring look different without Théoden's help? Absolutely. It is very possible that without the presence of Théoden and the rest of the people of Rohan, that Sauron and his allies might have won more victories. And that would've likely been devastating for those fighting Sauron in the War of the Ring. It might have been possible to win some battles without Théoden and his people, but they would've been hard to win and likely come at a cost. Fortunately, Gandalf was there to break the spell placed on Théoden, enabling him to regain his strength and fight against Saruman and Sauron. Because with his help, and that of the people of Rohan, including Éowyn, the War of the Ring went pretty well for those against Sauron. The Witch-King was destroyed, and Sauron was ultimately defeated. And that is likely thanks to Théoden and his people. Fortunately, they were present and were able to play a role in taking down the Dark Lord Sauron and all of his servants.
Of course, not every Lord of the Rings fan will agree. Some might not see Théoden and the people of Rohan as that crucial at all. Yet they played an important role in many battles. The Fellowship of the Ring and all others fighting Sauron owe a lot to them. Théoden's role in the battles in Lord of the Rings shouldn't be forgotten. Nor should the role of his people, including his nephew and niece Éomer and Éowyn.