De qual baddie da Terra Média eu estou pensando?

Todos, mas basicamente Morgoth começaram com boas intenções.

For nothing is evil in the beginning. Even Sauron was not so.

(Elrond, Conselho de Elrond)

Por um breve período após a Guerra da Ira, Sauron foi realmente 'bom' e queria reordenar a Terra-média e reparar seus ferimentos. Mas isso não durou muito tempo.

Very slowly, beginning with fair motives: the reorganising and rehabilitation of the ruin of Middle-earth, 'neglected by the gods', he becomes a reincarnation of Evil, and a thing lusting for Complete Power – and so consumed ever more fiercely with hate (especially of gods and Elves). Sauron was of course not 'evil' in origin. He was a 'spirit' corrupted by the Prime Dark Lord (the Prime sub-creative Rebel) Morgoth. He was given an opportunity of repentance, when Morgoth was overcome, but could not face the humiliation of recantation, and suing for pardon; and so his temporary turn to good and 'benevolence' ended in a greater relapse, until he became the main representative of Evil of later ages.

(letras)

Saruman, claro, começou bem: ele foi enviado pelos Valar como seu representante. Como Elrond estava apontando em minha primeira citação, o desejo pelo Anel corrompeu Saruman. Saruman era realmente muito parecido com Sauron:

Sauron had never reached this stage of nihilistic madness. He did not object to the existence of the world, so long as he could do what he liked with it. He still had the relics of positive purposes, that descended from the good of the nature in which he began: it had been his virtue (and therefore also the cause of his fall, and of his relapse) that he loved order and coordination, and disliked all confusion and wasteful friction. (It was the apparent will and power of Melkor to effect his designs quickly and masterfully that had first attracted Sauron to him.) Sauron had, in fact, been very like Saruman, and so still understood him quickly and could guess what he would be likely to think and do, even without the aid of palantiri or of spies; whereas Gandalf eluded and puzzled him.

(Mitos Transformados)

De acordo com Tolkien, Sauron era originalmente um servo de Aulë (basicamente o equivalente da Terra Média de Hefesto ) e, portanto, ele era um dos mocinhos:

Among those of his servants that have names the greatest was that spirit whom the Eldar called Sauron, or Gorthaur the Cruel. In his beginning he was of the Maiar of Aulë, and he remained mighty in the lore of that people. In all the deeds of Melkor the Morgoth upon Arda, in his vast works and in the deceits of his cunning, Sauron had a part, and was only less evil than his master in that for long he served another and not himself. But in after years he rose like a shadow of Morgoth and a ghost of his malice, and walked behind him on the same ruinous path down into the Void. - _{The Silmarillion}

And darkness he [Melkor of Morgoth] used most in his evil works upon Arda, and filled it with fear for all living things. Yet so great was the power of his uprising that in ages forgotten he contended with Manwë and all the Valar, and through long years in Arda held dominion over most of the lands of the Earth. But he was not alone. For of the Maiar many were drawn to his splendour in the days of his greatness, and remained in that allegiance down into his darkness; and others he corrupted afterwards to his service with lies and treacherous gifts. _{The Silmarillion}

Há alguma informação adicional em History of Middle Earth 10 sobre sua posição na casa de Aule:

Now Melkor knew of all that was done; for even then he had secret friends and spies among the Maiar whom he had converted to his cause, and of these the chief, as after became known, was Sauron, a great craftsman of the household of Aule.

e as razões da sua queda ...

Sauron had never reached this stage of nihilistic madness. He did not object to the existence of the world, so long as he could do what he liked with it. He still had the relics of positive purposes, that descended from the good of the nature in which he began: it had been his virtue (and therefore also the cause of his fall, and of his relapse) that he loved order and coordination, and disliked all confusion and wasteful friction ... all this ordering and planning and organization was the good of all inhabitants of Arda (even admitting Sauron's right to be their supreme lord), his 'plans', the idea coming from his own isolated mind, became the sole object of his will, and an end, the End, in itself.

Então, sim, ele realmente começou virtuoso e útil, embora bastante ingênuo. Foi só depois que ele ficou sob o domínio de Melkor que ele se transformou no bad boy residente da Terra Média.