• 
  Genevieve Kang

  baroneasa Goo
• 
  Anton Gillis-Adelman

  O'Seth
• 
  Dalila Bela

   Agent Olive (22 episodes, 2014)
• 
  Sean Michael Kyer

   Agent Oscar (30 episodes, 2014-2015)
• 
  Millie Davis

   Ms. O (31 episodes, 2014)
• 
  Peyton Kennedy

   Dr. O (15 episodes, 2014-2015)
• 
  Filip Geljo

   Agent Otto (33 episodes, 2014-2015)
• 
  Christian Distefano

  Agent Owen

• 
  Isaac Kragten

   Otis / ... (34 episodes, 2015-2017)
• 
  Anna Cathcart

  Agent Olympia
• 
  Olivia Presti

  32 episodes, 2016-2018
• 
  Michela Luci

  Agent Orchid
• 
  Alyssa Hidalgo

  Agent Orla
• 
  Alina Prijono

  Ophelia
• 
  Gavin MacIver-Wright

  Agent Oswald

• 
  Jayce Alexander

  Agent Omar
• 
  Eshaan Buadwal

  Olaf
• 
  Elijah Sandiford

  Agent Ocean
• 
  Valentina Herrera

  Agent Opal
• 
  Bryan Stevenson

  Oakley