Onox, also known as General Onox, is one of two main antagonists in Oracle of Seasons. He calls himself the "General of Darkness", and wishes to ruin the land of Holodrum in accordance with the wishes of his master, Twinrova. To do this, Onox is tasked with the burden of capturing the Oracle of Seasons and submerging the Temple of Seasons. Although Onox appears to be a giant in armor reminiscent of an Iron Knuckle, his true form is that of a dragon, summoned from the Dark Realm.
By capturing Din, the Oracle of Seasons, and encasing her in a crystal, Onox is able to submerge the Temple of Seasons into Subrosia and throw the flow of the seasons into chaos, resulting in the damage of the land and the weakening of the Maku Tree. To counter these events, Link sets out on a quest to obtain the Essences of Nature, which allow him to enter Onox's Castle on the Northern Peak to face him and revert his deeds.
After obtaining every Essence of Nature, Link goes the Northern Peak, where he uses their power to bust into Onox's Castle, breaking the protective barrier he had placed upon its entrance to bar intruders. Link faces Onox in two segments, the first in his natural form, using the comatose Din within a crystal to shield himself from Link's attacks. Before Link can defeat Onox, however, he reveals his second, true form to him. After defeating Onox, rather than cursing his own fate, he mocks Link as he dies, revealing that the Flame of Destruction has been lit, and Twinrova's grand scheme is one step closer to fruition.
If Link has already saved Nayru from Veran in Oracle of Ages, when Link reaches Onox at the top of the Onox's Castle, he will reveal to Link that Princess Zelda is already being prepared for sacrifice, so that Ganon can return.
And he is voiced by Kevin Michael Richardson in the English dub and Fumihiko Tachiki in the Japanese dub.