What does the man in decent attire represent to Goodman?
On a general level, the man in decent attire is Young Goodman Brown's companion on this unknown journey. This strange man also becomes a link to Brown's past, as the man explains that Brown's father and grandfather had made similar journeys.
It does become clear through imagery and symbolizm that the man in decent attire is, in fact, the devil. It is through this fact that Goodman Brown learns that all the people he regarded in such high esteem have their own links to the devil (Goody Cloyse, the minister, and the deacon).
The devil could then represent Goodman Brown's ability to give in to temptation and evil; therefore, having his own links with the devil.
He appears to be a older man than Goodman, somebody who carries a twisted, snake-life staff and seemingly to represent Goodman somewhat but not entirely and he was thought to be the object of Goodman's darker and ominous side of his life. He appears to be the "Devil" in the entire story, who claims to know Goodman's father and grandfather past had make similar wrong path to evil and temptation, like his grandfather participating in the persecution of the Quakes and his father, who had taken part in the assault of the Indian village. The man in decent attire actually symbolizes or is being compared to (imagery) the devil, Satan. It is trying to show that Goodman that appearances are deceiving to the eyes and people who you had trusted so much or have high regard to may have past connections with the Devil, like his father and grandfather, who had give in to temptation and power and went to the path of darkness, where evil reigns.