Step 1: Identify the comparison.
\nThe sentence is making a comparison using "no man in the city is so rich as he."\n\n
Step 2: Convert to Superlative Degree.
\nIn the superlative degree, we use the form "the + adjective + est" to indicate the highest degree. "Rich" becomes "richest" in the superlative form.\n\n
Step 3: Final Conversion.
\nThus, the correct superlative degree sentence is: "He is the richest man in the city."\n\n \n
Final Answer: \n\\[\n\\boxed{\\text{He is the richest man in the city.}}\n\\]