Titles like this are appositives: a construction where one noun phrase identifies an adjacent. Your question on comma use is almost a duplicate of this one, but a little broader, so I'll try to answer it in full. I'll quote the same style guideline as the top answer there:
Commas are used to set off an appositive when the appositive can only refer to a specific item. (The Chicago Manual of Style, 5:21,123; 6:22-24). Examples:
Mary's son, Jesus, is thought by many to be the Messiah. [Mary had only one son]
Dostoevsky's book Crime and Punishment is the great
books of all time. [Dostoevsky wrote more than one book]
Your sentences fall into the same two categories: presumably, Michael has only one boss, and there are multiple writers. Thus we would write
His boss, Michael, ...
The writer Michael...