13. Tig Kills Donna
Season 1, Episode 12: "The Sleep of Babies"
The original sin that sets much of Sons of Anarchy in motion happens before the series begins, when Clay sabotages John "J.T." Teller's motorcycle, killing Jax's father and necessitating a decades-long cover-up. But the crime that defines the show's first few years happens at the end of Season One, when Clay is led to believe that reluctant club member Opie has become a confidential informant for the ATF. So Tig is ordered to kill Opie; instead, he mistakenly shoots Opie's wife, Donna. The resulting attempt to throw the fellow Sons off the scent tears the club apart over the next few seasons, while the killing itself lets viewers know that the show was willing to play rough.