Harold, known to you as Dr. Mortimer, is coming to dinner on Tuesday.
A participle is a verb or verb phrase that is used as an adjective to describe a noun. In the correct sentence, the participial phrase is "known to you as Dr. Mortimer", and it describes who Harold is. The participle is "known".
The main verb phrase of the sentence is "is coming". It tells what Harold is doing. The other sentences do not have any participial phrases.