In Matt. 16:18 (KJV), it is written,
And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.
κἀγὼ δέ σοι λέγω ὅτι σὺ εἶ Πέτρος καὶ ἐπὶ ταύτῃ τῇ πέτρᾳ οἰκοδομήσω μου τὴν ἐκκλησίαν καὶ πύλαι ᾅδου οὐ κατισχύσουσιν αὐτῆς
What I know from Greek mythology is that ᾅδης (Hadēs) is the Greek god of the underworld, the god who becomes lonely and lives happily ever after with his queen Persephone. Why is Matthew taking a grim look at Hadēs?