Anton Yelchin, who played Chekhov in the reboot series:
http://www.tmz.com/2016/06/19/star-trek-anton-yelchin-dead/
Not that any character is easily replaced, or that anyone's death is trivial, but at least it was not Chris Pine (Kirk), Zachary Quinto (Spock) of Karl Urban (McCoy).
What is the most disturbing about it is the manner in which he died. It wasn't a collision, but a freak accident when he was completely by himself (see the article). One can't help but wonder if he lived for a while, and was conscious. I think that is what would trouble me the most: knowing you are trapped and cannot get out on your own, that your only hope is if someone comes along and discovers you before it's too late. Come to think of it though, if a Believer is in that position he'd have some really high quality time with God.
Fun fact (related but not): Anton Yelchin played Pavel Chekhov, not to be confused with Anton Chekhov, the Russian playwrite.