The Walking Dead burst on the TV scene in the fall of 2010 and quickly introduced fans into the show's brutality. There are some key deaths to major characters in the first season and even more in season 2, but an early season 3 episode changed The Walking Dead forever.
Of course, I'm referring to "Killer Within," the fourth episode of season 3. After Rick Grimes (Andrew Lincoln) led the gang to safety at the prison with some unfortunate hiccups, like Hershel getting bit by a walker, along the way, everything seemed like it was going to be okay for the first time since Dale (Jeffrey DeMunn) and Shane (Jon Bernthal) were killed and the horde of walkers took over Hershel's farm.
Immediately, The Walking Dead pulls the rug out from under these survivors and delivers its first truly devastating moment of the series, a moment that changed the series forever.

Lori's death was the first truly devastating moment in The Walking Dead
While Rick, Daryl (Norman Reedus), and Glenn (Steven Yeun) were fixing up the prison, Lori (Sarah Wayne Callies) led Hershel (Scott Wilson), Carol (Melissa McBride), Carl (Chandler Riggs), and Beth (Emily Kinney) out of the cell block. It's Hershel's first spin on crutches, and it goes south very quickly. One of the prisoners who escaped turns on the generators and opens a gate, which leads a horde of walkers into the common area outside the cell block.
Maggie (Lauren Cohan), Carl, and Lori end up in cell block C that's overrun with walkers, while Hershel and Beth get to safety in another part of the prison. T-Dog (IronE Singleton) and Carol try to fight off walkers and shut the gate, but T-Dog gets bit in the process. As devastating as T-Dog's death saving everyone is, it doesn't compare to what happens next.
Lori goes into labor during the chase. Without Hershel to perform the C-section safely, Maggie is forced to perform the surgery and save baby Judith. Unfortunately, Lori succumbs to her injuries.
I'll still remember when Maggie and Carl walk out of the cell block with the baby. It's forever seared in my brain, and I'm sure many Walking Dead fans feel the same. Watching Rick's devastation is incredibly hard to watch.
What makes matters even worse, there's no time to even mourn or take in the moment for these characters. Hershel, Carol, and Beth have a baby to help care for. Daryl and Maggie must make a supply run to find baby formula. Glenn has a group to protect and lead while Rick is out of commission.
It's a devastating sequence of events that is relatively unmatched in early Walking Dead. As far as major tragedies go in this series, this one was at the top of the list for a long time.
It also speaks to how good of a job Sarah Wayne Callies did as Lori. Most fans forget her character died so early in season 3. She made such an impact on this series in just a little more than 20 episodes.
Lori exiting the series completely changed the story, as well. The group now had a baby to care for during the apocalypse without her mother or access to medical care. Of course, we know things end up being okay, for lack of a better word for Judith, but it's clear that the show was never the same for Rick and the gang after this moment.

The Walking Dead season 3's tragedy paved the way for many other shocking moments
The Walking Dead changed after Lori's death, too. There are many horrible tragedies that happen in The Walking Dead. Up until Lori and T-Dog's death in season 3 episode 4, we said goodbye to Dale, Shane, Sophia, and Amy. None of those deaths hit as hard, or are nearly as shocking, as Lori's death.
After Lori's death, the horrors of The Walking Dead definitely increase. Over the next few seasons, we see some truly horrific and devastating moments and character deaths. To name a few, Hershel is beheaded by the Governor. Beth is killed by Dawn. Noah gets trapped in the revolving door. Glenn's death is a huge turning point for the franchise.
All of those moments would have hit even harder had The Walking Dead not killed off Lori and T-Dog in such a devastating and truly shocking way back in season 3.
While there's no doubt Lori and T-Dog's deaths in this episode were shocking, they weren't executed perfectly. Personally, I don't love that the show killed off Lori and T-Dog in this way so early into the third season. It's not that their deaths weren't earned, or anything like that. I'm fine with T-Dog and Lori dying eventually. I just hate that it happened this way, so early into the story.
Often, the mistakes the characters make often lead to the downfall of characters immediately after or later. Rick and the gang continued to take their foot off the gas when it came to their safety. It happened at the farm, and it happened directly after at the prison. It's not until the war with the Governor that Rick truly learns his lesson about keeping his people safe.
Overall, The Walking Dead season 3 episode 4, "Killer Within," remains one of the most horrific and truly devastating episodes of the entire series. There's no doubt it changed fans' expectations about what the creative team would do and how far they were willing to go to deliver a shocking, tragic moment.
