Castiel, the popular angel from Supernatural, was originally only planned to appear for a few episodes but later became a long-term ally of the Winchester brothers. His initial mission was to bring Dean back from Hell after his death and descent at the end of Season 3, thereby introducing angels and Heaven into the brothers' story.
This character retrospective mentions that Castiel was initially scheduled to exit the plot after appearing in just a few episodes. Some of the long-term narrative functions originally reserved for another angel, Anna Milton, were ultimately transferred to Castiel. The author believes that actor Misha Collins' chemistry with the main cast and the audience's response to the character prompted the writers to adjust subsequent plans.
As the series progressed, Castiel evolved from an enigmatic angel into a humorous ally willing to sacrifice for the Winchester brothers. He also defied Heaven, experienced a loss of control over his power, and attempted to make amends for his mistakes.
The retrospective also discusses Castiel's relationship with Dean and the fans' long-standing interpretations of their dynamic. The confession in the later seasons and the series finale remain topics of discussion surrounding this character.