In the fifth movie, Apollo appears to save his sister, Artemis from Seiya, and explains Seiya's question: Apollo doesn't show his personality, but how he continues Artemis plain, he must thinks like her: Is a god, and a superior being, so, he naturally has a right to govern the humans with no duties, and the human duties are just follow the gods with rights give by them. Apollo refuses to accept Seiya fight against a god, because if a god is the good and the certain by definition, the humans must follow them, ergo, fight against a god is incorrect. But Seiya refuses a existence and need of gods, but Apollo says Seiya must accept them.
Apollo with strong power, does some with Saori and Seiya, but, the sequel of the movie was cancelled, and we never will know what Apollo did. But in the final is shown a scene between Seiyas attack and the epilogue (Seiya and Saori in a secret garden), Seiya makes a scratch on Apollo's face.
He, together Artemis, is one of two representatives of the time (they do the day [sun] became night [moon] and vice versa) and may appear in the future.