As of October 2015, every season of “Castle” has introduced new characters. Some characters are recurring, while others only appear in a few episodes. The character of Jenny Ryan, played by Juliana Dever, was introduced in the second season. The character has appeared in several episodes across seasons.
The character of Josh Davidson, Kate Beckett’s boyfriend, was introduced in season three. The character last appeared in first episode of season four. In season four, Penny Johnson Jerald was introduced as Capt. Victoria Gates. She was one of the main cast members from season four to season seven.
The character of officer Troy Ellis, played by Maya Stojan, was introduced in season five. As of the seventh season, the character has appeared in 26 episodes. Lisa Edelstein played the character of Rachel McCord in season six and appeared in three episodes. In the seventh season, two new characters are introduced: CIA hacker Vikram Singh and private investigator Hayley Vargas.