Who is special counsel and former FBI director Robert Mueller?

Robert Mueller, who was named in late May as the special counsel to spearhead the FBI's investigation into Russian connections to the 2016 election "and related matters," has been in the headlines more than once since he was appointed. Most recently, President Donald Trump said if Mueller investigated his and his family’s personal finances, specifically those unrelated to Russia, it would cross a line.
Read more: https://www.yahoo.com/gma/special-counsel-robert-mueller-long-history-fbi-233504266--abc-news-topstories.html?source=Snapzu