Why does Mr. Gatz refuse to be called Mr. Gatsby?

In F. Scott Fitzgerald's novel The Great Gatsby, the title character's father appears in the final chapter of the book for the first time. With his appearance, many mysteries concerning Jay Gatsby are resolved, particularly those surrounding his background. 

An important revelation is that of Jay Gatsby's real name, in fact the same name as his father's: James Gatz. Mr. Gatz, who arrives to attend his son's funeral, does not like to be called Mr. Gatsby. This preference makes sense for two major reasons: 

1. Jay Gatsby was the creation and life of James Gatz Jr, not Sr. To Mr. Gatz, being called Mr. Gatsby means little or nothing because it was his son's dream, not his own. He feels no affiliation for the title. 


2. When Jay Gatsby took on his new name and identity, he rejected his past, and in doing so, clearly and symbolically rejected his father, whose name he abandoned. To be called Mr. Gatsby, the name for which he was rejected and by which he was replaced, is an emphasis on the hurt Mr. Gatz must have endured with the rejection by and disappearance of his son.