Baelfire

Baelfire is Rumplestiltskin's son, who appears in the episodes Desperate Souls and The Return.

Season One
Before Rumplestiltskin became the powerful sorcerer he is today, Baelfire was his only family and greatest treasure. Just a few days away from Baelfire's fourteenth birthday, all the children in the land are being forcefully drafted to fight in The Ogre Wars upon turning fourteen.

To prevent his son from being taken, Rumplestiltskin slays Zoso, "The Dark One", taking on his powers in an effort to be able to protect Baelfire. He brutually kills all the soldiers who attempt to recruit Baelfire, an act he relished in, which terrifies his son.

Later on in the The Return, his father ended the The Ogre Wars and saved thousand of childrens lives, but people are afraid of him and Baelfire wants things to back to the way they were. His friend Morraine tells him about the Reul Ghorm she heard of during war from eavesdropping on other soldiers. Baefire goes and finds the Reul Ghorm, which turns out to be the Blue Fairy. She gives him a magic bean to take him and his father to a "land without magic".

Baelfire takes his father into the woods and uses the magic bean, which creates a green, glowing portal. Rumplestiltskin is afraid of going to a place without magic or his powers, and backs out of the deal at the last moment. He lets go of his Baelfire, who calls him a coward before disappearing into the portal. Rumplestiltskin then calls for the Blue Fairy to help him get to his son, but it's no use as that was the last magic bean and he chose power over his only son. This has caused Rumplestiltskin to hate fairies, especially the Blue Fairy, because he blames her for taking away Baelfire, while she declared he was the one who drove off his own son.

So, he created the Dark Curse in order to be able to go to the same place Baelfire went. Even though the curse worked in transporting Rumplestiltskin into "a land without magic", he has not yet found his son in the last 28 years while in Storybrooke.

In the episode Skin Deep, Belle mentions finding children's old clothes in one of the rooms in the castle, which Rumplestiltskin says belongs to his son. Rumplestiltskin claims he lost Baelfire like he lost Baelfire's mother, meaning she also left or disappeared from his life in a similar fashion.

Trivia

 * Baelfire had been sent to a "land without magic" through the power of the magic bean prior to his father creating the Dark Curse.
 * He is the only person who his father has broken a deal with.
 * Rumplestiltskin's motivation in making the Dark Curse was to be able to go to the same world Baelfire was transported into. As the Blue Fairy warned, he would have to pay a very high price in order to be able to accomplish this.
 * His only friend seems to have been Morraine while all the other kids became too scared of him due to the reputation of his father, Rumplestiltskin.