Press chopped eggs in the bottom of a lightly greased 4 1/2-cup ring mold.
Combine mayonnaise and sour cream in a small mixing bowl, stirring well. Spread 1/2 cup of mayonnaise mixture evenly over eggs in mold; cover and refrigerate remaining mixture. Sprinkle three-fourths of caviar evenly over mayonnaise mixture in mold; cover and refrigerate remaining caviar. Sprinkle onion over caviar; press artichokes into mayonnaise mixture in mold. Cover and refrigerate overnight.
Unmold ring onto a serving platter. Spread reserved mayonnaise mixture over surface of ring; sprinkle with reserved caviar. Serve with assorted crackers.