If you are playing Torchlight II with mods enabled, you will find that characters you have created during an un-modded gaming session are not available from the character selection screen. To access your previously-created characters, you will need to launch Torchlight II in "vanilla" mode without mods.
It is possible to copy your saves over from an un-modded state to enable mod access, but be advised that we cannot guarantee that it will work flawlessly, particularly if you take a character from a modded state and bring it back into an un-modded mode of gameplay.
Your modded character saves are stored in Documents\My Games\Runic Games\Torchlight 2\ModSave or (Documents\My Games\Runic Games\Torchlight 2\ModSave\7458XXXXXXXXXXXXX) for Steam users.