Dumbledore and Gandalf
Dumbledore and Gandalf both embody the elderly wizard mentor, following in Merlin's footsteps. They guide the main character on their journey to defeat evil and help them fulfill their destiny. Both are the representation of good in the story, and they both had a moment when they had to choose between being a force of good or having immense power. Though some might say that as people Dumbledore and Gandalf may not be perfect and ultimate good but in the stories they are the representation of the force of good and it is their choices that help them lead as an example for the side of good. Dumbledore and Gandalf also have a similar look; long white/gray hair and beard, and adorned in a robe. They both also have objects that they funnel their magic through; Dumbledore has his wand and Gandalf has his staff. The last similarity is that they both die and come back from death to support the main character on their journey, though Gandalf comes back in a more physical way and Dumbledore comes back in a spiritual way.
Harry Potter and Frodo Baggins
The young man, or hobbit, who sacrifices themselves for the greater good. They both go on journeys to destroy or rid the world of evil. They both must destroy objects that the evil character's soul is connected to, and they both have to struggle against evil trying to take over their mind and soul. As far as appearance goes, they have similar hair color and they are both smaller than the adult characters. Also, they both have to grow when it comes to worldly experience. Harry and Frodo are thrust into a fight against evil, as well as an unknown world, when they are young. Lastly, they both feel a kind of calling or destiny that it is their purpose; to destroy the evil plaguing their world.
Ron Weasley and Samwise Gamgee
Harry and Frodo would not have gone far without their best friends Ron and Sam. Ron and Sam come from a non-privileged background, and they have known Harry and Sam, respectively, since boyhood. They must watch while their best friend is tormented by evil, and know that one day that friend must face the evil and that he might not come back alive. Ron and Sam are both tempted by evil and they both must overcome and choose not to give in to evil forces. In appearance, they are similar; they have similar coloring, they are both pale, and Ron has red hair while Sam has strawberry blond hair. Either way, they have opposite coloring from Harry and Frodo, and they also have a larger stature then their best friends.
The Order of the Phoenix and The Forces of Good in Lord of the Rings
In both Harry Potter and Lord of the Rings, there are the many followers of good. In Harry Potter, the group fighting for good is The Order of The Phoenix. Dumbledore is their leader, and they fight the Death eaters. In Lord of the Rings the people fighting for good do not have a collective group name, but they would be the armies of Gondor and Rohan, and their leaders are Aragorn and Gandalf. The elves are also on the side of good. In both film series, the fighters of evil are individuals and the audience identifies with them, so when one of them dies or is injured, the audience cares and becomes sad. Also, the audience must root for the forces of good, so they need to be relatable as well as accessible, and both film series have accomplished that.
Lord Voldemort and Sauron
Lord Voldemort and Sauron are the representation of ultimate evil. Neither of them care about life, but they simply want power and to rule over all beings. They were both powerful at one time, then they were defeated but they were not killed. They reverted to a less than human form and waited to be returned to their full strength. The reason why they could not be killed the first time was that they had connected their soul to objects; Voldemort in seven horcruxs, Sauron in the ring. Also before they can be truly killed, the object that contains part of their soul must be destroyed. They have no gray area, they are pure evil.
Evil's Assistant
The bad guy always has a stooge or a follower who joins their side, either because they are bad or because they believe that they have joined the winning side, but is not really prepared for whether the bad guy wins or loses. In Harry Potter, Lord Voldemort had many followers but Lucius Malfoy and Bellatrix Lastrange are examples of the stooge and the follower who may be just as evil as their master. Bellatrix Lastrange is the example of the follower who is also pure evil, but not as powerful as their master. Lucius Malfoy is the classic example of the stooge, as he joins Lord Voldemort's follower because he believed that Voldemort would end up on top and he wanted to be on the winning side. In the end, he is not really evil but he is not a nice person either, and he is not prepared for the world that Voldemort would create if he won. Malfoy becomes afraid and disheveled, and by the end he has no real power or influence in any circles. In Lord of the Rings, the Sauron's stooge is Saruman. Saruman is a wizard who joined Sauron's side because he believe that he would be victorious and have all the power. He, like Malfoy, did not seem to really think about what the world was going to be like if Sauron won, and in the end he is stripped of all of his power and becomes disheveled and broken.
Death Eaters and Orcs
Every villain needs an army, and in Harry Potter, Voldemort's army is the Death Eaters, while in Lord of the Rings, Sauron has his army of Orcs. In both cases, the evil armies are dehumanized; the Death Eaters by their masks, and Orcs are not human. This is one reason why the audience in general will not relate to the evil armies. The Death Eaters and the Orcs follow their evil leader willingly and take pleasure in doing his bidding. They enjoy killing the good guys as well as torturing them.
Conclusion
In the end, Harry Potter and Lord of the Rings have many similar characters because they are both stories about good triumphing over evil. Both of the franchises have become extremely popular all over the world, and one would wonder why the underlining theme of good versus evil is something that people relate to. One reason would be that in these stories, evil is easily identified and one can destroy that evil. The real world is not black and white, and there are a lot of gray areas. In the good versus evil stories, the world is mostly black and white with very little gray area; one always knows the enemy. Most people would like it if the bad guys would walk around with a sign on their forehead saying "do not trust me I am a bad person," but unfortunately they do not. Also, in the good versus evil stories, good always wins no matter what happens, while in the real world that does not always happen, and sometimes it feels as if evil always wins. Because good always triumphs over evil in these stories it gives the viewer some comfort that no matter what happens during the journey the good guys will not die in vane because the evil will be defeated in the end. This may be why there is a universal draw to the Harry Potter and Lord of the Rings stories, because they are each a classic tale of good defeating evil and at a basic level they depict how the general population of the world wishes the world could be, evil being easily identifiable and good always victorious.