A full list of the characters are below, along with details on how to unlock or purchase each one. Where it says 'find' a certain number of a particular item, you have to do this by locating Mystery Chests and getting lucky with the contents in there.
Find 50 Stereos
Find 200 Spike Guitars tokens
Find 3 Hats
Find 500 Yutani UFOs tokens
The list of characters is quite extensive
You can still get these characters even after the time has passed by changing the Time and Date in your device's settings. For more information on this, see this guide's Cheats section.
Zombie Jake (Halloween)
Elf Tricky (Holiday)
Tony (New York)
Eddy (New Orleans)
The game also provides numerous limited edition characters depending on the game's current scenario and setting
There are a variety of characters available in Subway Surfers, with more added every time a new update or variant of the game is released. If you would like to be able to unlock one of the limited characters but the time of that offer has passed, you are able to do so by changing the clock on your device. For more information on this, check out this guide's Cheats section.