The Extended Edition of The Desolation of Smaug confirms Gandalf the Grey's fears of Smaug being in league with Sauron as Thráin reveals in Dol Guldur. Should the Dragon have survived its attack upon Lake-town, then the Dark Lord would have used him to devastating effect against the Free Peoples in the North.
Smaug could easily have cut through the armies of Mordor, and delayed the invasion of Middle-earth by years. So it wasn't in Sauron's interest to take on the dragon, but that doesn't mean he saw it as a lost cause, as he fully planned on creating an alliance.
Peter Jackson certainly makes the assertion in the theatrical and extended editions of the Hobbit movies that Smaug and Sauron are not only well aware of each other, but are planning to ally with each other.
Sauron's main objective in The Lord of the Rings was to reclaim his One Ring and dominate Middle-earth, but his true plans may have gone beyond this. Sauron's ultimate goal might have been to free Morgoth, his old master, from the void and rule alongside him, or to obtain the power of the Flame of Anor.
That title falls to Ancalagon the Black, the largest dragon ever to have existed in Middle-earth. He was bred by Morgoth during the First Age to fight for the Dark Lord during his campaign of terror.
Gandalf's main reason for supporting Thorin's quest in The Hobbit was to eliminate the threat of the dragon Smaug, who would be a powerful ally for Sauron. Despite popular belief, the Balrog known as Durin's Bane was more powerful than Smaug in Middle-earth, being a literal, primordial demon.
Saving Galadriel at sea was likely a method of gaining her trust, since Sauron would need an Elf's friendship to enter their realm. Whether he targeted Galadriel specifically because he could exploit her bloody-minded rage and broken heart is unclear.
The outcome is that Galadriel is able to penetrate Sauron's mind and issues a single command "Go back to the void from whence you came!" Unable to resist her any longer, Sauron screams and flees with the Nine.
With Frodo being hunted by the Nazgul and running from the Shire in The Lord of the Rings, Sauron learned two key things: a Hobbit was carrying his One Ring, and it was being delivered to Rivendell.
There is no direct link between Smaug and Sauron, but there is an indirect connection. Back in the First Age, Sauron was Morgoth's chief lieutenant. In this same period Morgoth bred the dragons, with the mighty Glaurung being the first.
Although Smaug was the greatest of the Dragons of his day, he seems not to have been the last of his kind as Gandalf told Frodo Baggins that "there is not now any dragon left on earth in which the old fire is hot enough [to melt the Rings of Power]", indicating the presence of other, lesser dragons.
Despite Smaug's great size, strength and Durable hide, Sauron's Dark Magic, Powerful Weaponry and Great Intelligence ultimately triumphed over Smaug. Sauron was immune to Smaug's fire as Sauron has control over fire and had adapted to it.
Smaug's dragon-fine would not have been hot enough to destroy the One Ring. The malevolence that Sauron put inside of the Ring could only be destroyed in the Cracks of Doom, so Frodo was compelled to make the journey to Mordor.
According to the book, he never saw Bilbo. Bilbo was there, in the same hall, under the same roof but he careful enough to stay in the shadows and wear the ring. Smaug could smell him and he knew where he stood but never asked him about his invisibility.
In his notes, Tolkien remarks that Sauron saw Galadriel as his equal. Add that to the fact that she's untrusting of Sauron (yes, even when he's in his Annatar guise) and an unwavering, single-minded force, and it's more likely than not that Sauron feared Galadriel — or the potential she held to upend his plans.
Additionally, while he was in his weakened state, Galadriel could hold him off through the power of will alone. However, if Sauron had his One Ring and faced off in a battle against Galadriel, it's unlikely that there would be much she could do.
Thus, Galadriel's dark form in Jackson's The Lord of the Rings personified what would have occurred had the Lady of Lothlorien given in to temptation and taken the One Ring for herself. She would have succumbed to evil because the Ring was indomitable, even with her power.
With that in mind, Galadriel and Sauron's longing gazes were a big stretch, at least in the context of romance. Still, The Rings of Power's proposal scene wasn't completely out of left field. Sauron seemed to genuinely feel a connection to her, and part of that came from sensing the darkness inside of Galadriel.
Despite feeling some possible temptation from Sauron's offer to become his Dark Queen, Galadriel's denial of the Dark Lord shows she can't be so easily swayed. However, that doesn't mean Sauron still won't try to trick her into helping him gain the power he's destined to obtain in Middle-earth's Second Age.
Balerion was obviously the dragon of all the dragons, a monster. How many dragons, and which ones do you think it would take to fight him and stand a chance? I think he'd be annihilated with a combination of Caraxes, Meleys and Verithmor. All three are experienced and very vicious dragons.
Later Balerion easily killed his kin Quicksilver, alongside his rider Aegon, during the Battle Beneath God's Eye. Balerion lived to be two hundred years old, dying of old age during the reign of Aegon's grandson, King Jaehaerys I. His last rider was then-Prince Viserys I Targaryen, who claimed him in 93 AC.
One of the skulls is 3,000 years old, so it is definitely from Old Valyria. Yet it isn't the biggest one, the biggest is Balerion's skull. Maybe, there're some other skulls of Targaryen dragons from Old Valyria, but they don't surpass in size the skull of Balerion the Black Dread.
