Oberon is arrogant and harsh but is not a tyrant, this makes him an interesting opponent to the clan as he was not blatantly evil or criminal: however he cared little for people who stood in his path and was very stubborn once he had made his mind up on a matter.
Oberon was also incredibly powerful, far surpassing even other Children of Oberon - his power only served to make him more dangerous and he easily defeated those that stood in his way - yet even Oberon was no match for the desperation of a mother's love as Fox unleashed previously unknown magic upon Oberon in an attempt to save her son, succeeding in blasting the misguided being through a castle wall.
This provided Goliath with the distraction he needed to try and convince Oberon that Alex could be left in the human world and still be taught the ways of magic, Oberon eventually agreed to this and left - yet he showed his more vindictive side when he punished Puck for his part in opposing him by banishing him forever from Avalon and removing all of his magic save for that which was needed to protect or teach Alexander.
Prior to these events Oberon had also faced the Gargoyles in battle (albeit in a weakened form) on Avalon when he became angered by the presence of the Avalon Clan and sought to destroy them if they wouldn't leave - however his wrath was subsided by Titania, who offered an alternative and Oberon fought the clan in a weakened-state (presumably to prevent the issue of facing a godlike entity).
Yet even in his weakened-form he managed to defeat the gargoyles and it was only through trickery on Titania's part did they manage to finally defeat him by using an iron bell, however instead of destroying the powerful being they made a deal with him that in return for his promise to stop attacking them they would not use the iron bell on him or his Children again.
Oberon was taken by this act of mercy and not only agreed to the terms but decided to make the Avalon Clan his new guards and granted them immunity from his magic.