Why were these characters invited to 'Dead's' dead reunion?

Spoiler alert! This story contains plot details from Sunday's episode of AMC's The Walking Dead.

Tyreese Williams (Chad L. Coleman) certainly didn't die alone. The sensitive, humane Walking Dead character, worn down after witnessing so much brutality and death, convened an imagined mini-conference on how to live one's life in his final moments, as he succumbed to the bite of a walker.

The previously deceased Dead characters who gathered in a small bedroom, at least in Tyreese's mind, all had a reason for being there, executive producer Scott M. Gimple says. He explains:

"These are all people who had some major significance for Tyreese.”

The attendees included:

Beth Greene (Emily Kinney)

Beth's killing devastates everyone in the group. "Losing Beth, being there when it happened, tore him apart," Gimple says.

 The Governor (David Morrissey)

Tyreese had lived in The Governor's Woodbury, a sanctuary built on bad deeds, before changing teams and siding with Rick Grimes and his group. "The Governor was somebody Tyreese initially threw in with," Gimple says.

Bob Stookey (Lawrence Gilliard Jr.)

Tyreese "had to kill Bob," Gimple says. He spared his sister, Sasha, who was involved with Bob, from having to do it.

Lizzie and Mika Samuels (Brighton Sharbino and Kyla Kenedy)

Tyreese looked after Lizzie and Mika after the prison was destroyed. After Lizzie killed Mika, Carol (Melissa McBride) decided Lizzie has to die to protect baby Judith. "Lizzie and Mika are two people that very much challenged his outlook," Gimple says.

Martin (Chris Coy)

Tyreese and Carol captured Terminus foe Martin. While being held captive, Martin told Tyreese his decency would be the death of him. "Martin was somebody he had a very intense conversation with. Martin was saying, “Dude, you’re not going to make it,’ " Gimple says.

Gimple is happy that the reunion remained an unspoiled surprise for viewers.

Arranging the guest appearances and keeping them under wraps "was a very delicate process," he says. "Brighton and Kyla are pretty distinctive looking people. Like, why are there two little girls walking around on set? When I started working on it, I remember calling people and immediately being like, 'Hey, not to freak anybody out, but could you check if David Morrissey is available?'  I was so psyched we got everybody we wanted for that sequence."