0
No, the actress Krysten Ritter is not related to the late actor John Ritter.
Laszlo Ritter's birth name is Lszl Ritter.
John Ritter's father was country western singer and actor Tex Ritter and actress Dorothy Fay (Southworth). He was NOT related to Thelma Ritter.
John Ritter's son s Jason Ritter.
However, Josh Ritter is a singer/songwriter born in Idaho.