6. Kal Penn (Dr. Lawrence Kutner) - House
While most TV shows forced to deal with an actor's sudden departure at least try to contrive an organic reason for their exit, House did something incredibly daring and divisive with Dr. Lawrence Kutner (Kal Penn).
Penn's Kutner joined the show in season four, but his tenure was cut jarringly short near the end of season five when he was found dead from a self-inflicted gunshot wound.
Fans were naturally shocked, though it transpired that Penn had actually accepted a job at the White House under the Obama administration and so required a hasty write-out.
The showrunners could've easily had him leave for any manner of reasons, though instead used the opportunity to make a stunning statement on mental health - that even a person as seemingly well-adjusted as Kutner can be suffering internally.
Fans remain intensely split on the decision, but if nothing else it highlighted the tendency for suicide to blindside those left in its wake.