Watching Travelers (2016) reminded me of this bit from Robot Chicken that is mocking the Battlestar Galactica reboot and how so many characters were eventually revealed to be cylons. It sort of seemed like the writers of Travelers had used "just make the character a traveler" as an excuse to help whenever they had written themselves into a corner or something.
Aside from the characters who were pretty much always travelers, this is who I can think of off the top of my head:
Travelers spoilers
- McLaren's FBI partner from the first season became a traveler for the second season
- Carly's ex-boyfriend became a solo traveler for the last season
- Trevor's guidance counsellor becomes a programmer traveler who is nearly another main character starting with the end of the first season
- Philip's girlfriend turns out to be a faction traveler (granted we certainly knew she was a traveler from her introduction, it was the fact that she was actually faction that was the twist)
- Traveler 001 jumps around to a bunch of different hosts, most notably Dr. Perrow
- that podcaster news guy got turned into a traveler so he would stop being a nuisance to the grand plan
Robot Chicken S4E1 "Help Me": https://www.youtube.com/watch?v=FzH6GVBSXSk