In which season does Rick Grimes depart from the main series?

Rick Grimes departs from the main series in Season 9 of The Walking Dead. Andrew Lincoln, who played Rick from the premiere onward, appears in the season's first five episodes before the character disappears after being seriously injured and presumed dead by the other survivors.

Rick is thrown from his horse and impaled on rebar while trying to stop two approaching walker herds. Rather than showing a conventional death, the story has him destroy a bridge to divert the walkers, apparently sacrificing himself. In reality, Anne/Jadis finds him alive and arranges for his evacuation by helicopter, setting up later stories outside the main series.

A common mix-up is saying Season 8, because Lincoln had considered leaving around that time and Rick's storyline was heavily foreshadowed then. However, the character's actual departure occurs in Season 9, which was Lincoln's final season as a regular lead. Rick later returns briefly in the series finale and continues in the spin-off The Walking Dead: The Ones Who Live.