Jack Hotchner

His first appearance was in The Fox, when his parents introduced him to the team as a newborn. He was not seen until Machismo and then in In Name and Blood, the last time he will be living with both his parents in the same house.

From then on we see little glimpses of him when his father visits him (Seven Seconds) or when he gets to watch some homemade videos he keeps with him, like in Pleasure is my Business, until Faceless, Nameless when Hotch must say goodbye to him because his mother and him are placed under witness protection after being threatened by Foyet.

His next appearence is again in video format, this time shown to Hotch by Sam Kessmeyer in the episode Reckoner, and we learn his birthday is that day or a near previous one.

In 100 he's seen with his mother in an unknown location when she gets tricked by Foyet to come back to their home, where he's waiting for them. In his eagerness to make Hotch suffer, Foyet allows a lenghty phone call between Haley, Hotch and Jack, and his father gets to tell him to "work the case", a code phrase for him to hide in a bin and wait for his dad to get him, which will be fundamental to save his life.

We see him for the last time in The Slave of Duty, first at his mom funeral and wake and later with his dad at the condo where they are going to live together; in a couple of secuences it's revealed how much he miss his mom and that he thinks his daddy is like Captain America.