Who is Richieu Spiegelman from The Complete Maus and what is their importance?

Vladek and Anja Spiegelman's first child, a boy, Richieu is born during October 1937 and died c. 1941 though the date is not specified in the text. Vladek describes Richieu as a beautiful and intelligent child. Richieu lives with his parents until c. 1940-1941 when they send him to live in Zawiercie under the care of his aunt Tosha. He is sent away because his parents perceive Zawiercie to be a more secure location than their current ghetto. Unfortunately the Nazis eliminate Zawiercie. Hours before being evacuated to Auschwitz, Tosha gathers Richieu, her own daughter, and other infants in her care and mercifully kills them by using poison, thus sparing them the horrors of Nazi brutality and sure execution. Although they obviously never met, Artie feels a complex sibling rivalry with Richieu which is detailed in the graphic text.