thank you for your comment.
Now, I do have a few things I want to say though:
1. Sauron, unlike Melkor, did not exactly "spread" his powers onto other things. Saruman was a fool, and did exactly that, resulting in him losing a lot of his powers, when he terraformed Isengard. And Melkor spent so much of his power, that by the end of the first age he was weaker then Sauron with the one ring.
However, Sauron was no fool.
Sauron knew not to weaken himself on purpose.
The ring is an ancour, and while he is in possesion of it, it strengthen him. However, it's absence does not WEAKEN him.
Third age sauron, barring his shapeshifting ability that was lost after the fall of Numenor, was on an equal footing as his former self in the first age.
The ring never took away power from him, just gave him additional power.
And as we know for a fact that a decent number of 1st age elven lords were more then capable of fighting against someone of his level, we can say for sure that there are amongst the Eldar those who can defeat him.
Fingolfin gravely wounded Morgoth, who at the time was still on the level of a Vala, light-years beyond the likes of Sauron.
Feanor fought against an entire legion of Balrogs, and drove them away in his madness.
Ecthalion killed Gothmog, who was the physically superior between the generals of Angband, and he did so while wounded, and after fighting a dragon with Tuor.
Earnedill Slew Ancalagon the Black, who was stated to be the mightiest of all of Morgoth's servants.
Luthien and Huan single handedly beat Sauron up, and Huan, while a mighty spirit, was not even a maia, let along a vala, and Luthien was a "mere" half maia half elven royalty.
Finrod Felagund, before Luthien and Huan, fought alone against Sauron, and they were mostly evenly matched.
By the time of the third age, the reason non could contest with him is that non of the great elves remained.
Cirdan, Galadriel and Elrond were all mighty and powerful, but even Galadriel, who was of Noldorian royalty, by that time was already old and weakened, and to begin with was never a true match to her siblings and other great family members.
Even without the ring, Sauron was the mightiest being in Arda at the third age, simply because all of the great mortals have passed away long ago, and non of the immortal spirits who could contest with him remained in this realm.
However, in the first age?
And before?
Sauron was not very impressive for many.
Sure, he was terrifying, and great in power, but his biggest strength was that he knew the limits of his power, and relied on his intelligence and sharp mind to win, rather then stregth, as the first age was full of people of equal, and greater statur of his.
The third age was when non could contest him but very few, and even they would lose in his presence, such as Gandalf and Galadriel.
with falling to the ring, again, only in the third age.
Before, in, for example, the first age, the power of the will was so great that a "mere elf" managed to wound the mightiest of the Valar!
This is a feat beyond anything Sauron can even scale to, honestly.
2. I agree about Sam, but you have to remember: his humbleness, stubborness, dumbness, and his undying loyalty to Frodo, all accumulated in a fierce mind and a near unbreakable force of will, which played a great rule in overcoming, even if temporarily, the effects of the ring and it's corruption.
3. Gandalf is not the mightiest Istari period.
That is Saruman.
Gandalf was, if not the weakest, on the weaker side of them.
Olorin as well was a relatively weak maia, and a coward, that it.
He was humble because he understood his weakness, and the fact that his brain and empathy are his biggest weapons.
He was an advisor to the elves in secret, and was used to travel long distances across all of Arda, unseen.
He was never meant to be sent, but was sent anyway by Manwe's order with the other four to act as a sort of a balancing force, the same as Radagast, who was sent as a balancing force that was supposed to calm Saruman.
When Gandalf returned as Gandalf the White, as he said himself, "I am Saruman".
He recived the powers and position Saruman held, with a slight boost.
He won such a power from Eru by showing his bravery, and his resolve to the mission, and not for his humility.
As of the ring, yes, his humility did play a major rule here.
He was humble enough to understand his place in the world.
He was terrified from Sauron's power and might, and he knew very well that he could never truely control the ring, and it would corrupt him if he ever attempted to lay a finger on it.
What took Galadriel a long time and preperation, took Gandalf only a split second of thought, which is what distinguished him from the rest of the Istari, and from the rest of the characters.
But this is not the reason he became so powerful, and ended up being the mightiest being in all of Arda, after Sauron.
The reason, again, was his resolve and loyalty to the cause.
And this resolve and loyalty came from someplace.
and it's his humanity.
Gandalf is the most human character in all of the Legendarium, in my opinion, and it is to be expected, considering how long he has been amongst humans.
His love for the hobbits, his love for his life, and for the simple things around him, for humanity, for the middle earth, for all of the livings, and his very human traits, were the thing that caused him to be so loyal.
Even as the Maia Olorin, he was very much human, more so then any of them.
After all, his adventures in the middle earth did not start with him as Gandalf, but he did so for Eons before they sent him.
He lived side by side with mortals, gave them council, helped them in their trials, and learned their ways.
At the same time, he learned from the wise Neinna grief, mercy and humility, and from the wise Irmo about dreams, desires and passion.
He was defentially the most human of them, and understood very well the world around him, which also led to his humility and wisdom, which in turn led to his great force of will, bravery, and his ability to refuse, at least initially, to the temptation of the ring.
