Nero
Nero is the protagonist of Devil May Cry 4 and is the player for most of the game. Little is known of his origins, or where he got his demonic arm from, but there are many references (Sanctus makes a few and the birds of a feather mission) that Nero is a decendant of Sparda. He was orphaned at a young age and taken in by Kyrie and Credo. He was inducted into the Order of the Sword, a band of religious knights that worship Sparda. His unique talents and personality mean he normally takes care of the more unusual jobs. He and Kyrie fall in love at some point and this is what drives him on. He is sent by Credo to apprehend Dante at the start of the game, but soon uncovers a much more sinister plot involving Sanctus' and Agnus' Savior. He is sucked inside it and is trapped for a time before Dante frees him and he manages to kill Sanctus and stop the Savior from within.
Dante
Dante, the main playable character from the rest of the series makes a nuch kesser appearence in this game. For much of the game he is viewed as a bad guy and is a boss on two occasions, but helps Nero. He is the son of the demonic lord Sparda and therefore possibly related to Nero. He runs the Devil May Cry shop along with Lady and Trish, who hunt down demons for a living. Dante in the opening cutscene to burst into a sermon by Sanctus and shoot him through the head, although it turns out to be a demon. After a brief fight against Nero he leaves, then reappears later to reclaim his brothers sword Yamato.
Kyrie
Kyrie was born and raised in the town of Fortuna. She is Credos brother and Neros lover. She is appointed as Songstress for the Festival of the Sword celebrating Sparda and is heard singing in the opening video. She often wears a necklace that was given to her by Nero. She dispairs of the fact that Nero and Credo are always fighting and is upset when she finds them at each others throats. She is kidnapped by Agnus to try to force Nero to cooperate and used to power the gigantic Savior, before Nero rescues her.
Credo
Credo is the head of the Order of the Sword. He serves as a close advisor to Sanctus and dislikes Agnus. He is Neros superior and adoptive brother but doesn't get along with him that much. He changes into Alto Credo to fight Nero but loses and gives uo the Aegis shield. When he discovers that Sanctus is using Kyrie in his evil plans Credo betrays him and fights him to give Nero time to stop the Savior. Samctus stabs him with Yamato and Credo is mortally wounded. His last wish is for Dante to save Nero and Kyrie.