Issac

Issac is an original character and minor character.

Pre-Apocalypse
Nothing is known about Issac's life before the apocalypse.

Post-Apocalypse
At some point, Issac joined the Constantine Safe-Zone.

Between the Cracks
Issac first appears sitting with Matt, Kaitlyn, and Sal having lunch when Matt is introduced to him. Issac however, gets freaked out by Matt's crowbar arm and leaves to Matt's sadness.

Sal
While not interacting much, it can be assumed Sal and Issac have a mutual bond towards each other.

Kaitlyn
While not interacting much, it can be assumed Kaitlyn and Issac have a mutual bond towards each other.

Matthias "Matt" Harris
While only interacting briefly, it can be assumed Issac is paranoid of Matt due to his crowbar arm.

Trivia

 * Issac is the youngest character to appear in the series, at age nine.
 * Additionally, he is the third character to have a confirmed age, after Leon and Matt.