The 3 toughest characters in popular fiction not named Jack Reacher

Joe Ledger

Former US Army Ranger and Policeman Leger finds himself working for a clandestine US Government department that deals with threats of a highly scientific nature. A couple of cases Leger worked on are weaponised zombie and Human/Animal hybrids. In the end Ledger and his comrades always come out on top.

Scot Harvath

Ex US Secret Service man turned deniable black ops agent Harvath has dealt with an number of threats to the USA. A Russian steatlh attack, a terrorist attack on Manhattan and stopping an ancient virus being weapoinised. Harvath will enact a brutal form of justice on those who endanger both US citizens and soil.

Louis

For once not the main character in the series he appears in Louis is very important on John Connolly's Charlie Parker novels. In that anyone who wishes to do harm on Parker then they will find themselves dealing with Louis and his (in more ways than one) Angel and the former is a very proficient killer. Connolly turns his focus on Louis's past in the novel The Reapers.