Guy Boucher was quite a controversial figure in Ottawa. He coached them from 2016-17 to 2018-19 where he was fired after poor performance.
The Senators made the 2017 Eastern Conference Finals under Boucher and fell to the eventual Stanley Cup Champion Penguins after a game 7 overtime loss.
Boucher will look for a fresh start in Toronto where he will try to help the Leafs to a Stanley Cup, a goal the Senators could not reach.
In addition to hiring Boucher, the Leafs also brought on Mike Van Ryn who previously played for them.