Ensemble Darkhorse: Originally scheduled to die in his first episode, turned into one of the most memorable things in the show.
The Fog of Ages/Time Abyss: Methos isn't even sure how old he is. His memory goes back five thousand years and "before that, it all starts to blur." Joe Dawson describes him as "An Immortal who's so old, he can't remember the time of his birth."
Retired Monster: Even has one of the page quotes. However unlike the classic Retired Monster he is sorry and wants to atone by destroying his comrades.
Underestimating Badassery: Several people have underestimated him because he usually avoids conflict. In one case, a possessive immortal who hates that Methos slept with his slave tracks him down in the present day, using both Joe Dawson and Joe's daughter as bait. Said immortal thinks Methos is a weakling and a coward, and expects to easily beat him. Instead Methos curb stomps him, and the last words the other immortal hears is Methos saying "Just because someone doesn't like to fight doesn't mean they can't."
Also, in the bad timeline shown in the last episodes where Duncan was never born, Methos went on one hell of a Roaring Rampage of Revenge when the Watchers are taken over by Horton, who begins slaughtering immortals and kills Methos' mortal lover in an attempt to get to him. Methos promptly teams back up with his old partner Kronos and begins leading the war against the Watchers. Their actions are described thusly: "They made the Russian Mafia look like choir boys."
What Could Have Been: Methos was slated to die but the producers like what the character brought to the series and he became a recurring character.
Would Hit a Girl: He has been alive for thousands of years before the idea of chivalry, after all.
He might have done this for fun when he was Death of the Horsemen, but in the present? They're gonna need to deserve it a lot.
Ax Crazy: After Duncan is afflicted by the Dark Quickening and tries to kill him, Richie decides to devote himself to The Game, and goes on a nationwide Immortal killing spree.
Dawson Casting: Not so noticeable at first, but by the end of Richie's time on the show, Stan Kirsch was pushing thirty. Richie became Immortal at age nineteen.