Yakone

Yukon was a man who threatened Republic City fourty-two years before Avatar Korra's arrival.

History
When Yukon threatened Republic City in 128 ASC, Avatar Aang "[dealt] with him" head-on.

Fourty-two years later, Councilman Tarrlok brought him up in an argument with Tenzin as an example to gather support from the other United Republic Council members to approve sending in a task force to attack Amon head-on, just like Avatar Aang had done all those years ago.