Forgot log in name

When you went through the reset password steps in the Recovery Partition, you had to select a user. Weren't you able to see your user name there?

Sometimes it is not possible to log in your user if you forgot its password. In that case, you are forced to reset the password through OS X Recovery.

1. Press Command and R keys while your Mac is starting up and hold those keys until you see the Apple icon. If you have a Mac with Internet Recovery, read -> http://support.apple.com/kb/HT4718. If your Mac has got a wireless keyboard, press them when you hear the startup sound.
2. Once you see the "OS X Utilities" window, go to Utilities -> Terminal, and type:

resetpassword

Press your user and type your password. Finally, reboot, and you will have changed the user password successfully.

User Password Reset

Enter your full name, if you entered that full name when you created the user. That full name will work at the login box, in addition to the shorter login name that most folks use. This will be the easiest, if you gave your Mac a name you remember when you created your login.

If you don't remember...

If you don't have files and apps installed—files and apps that can't be recovered from a Time Machine backup, or from the Mac App Store or another source—wipe the disk from Recovery, and reinstall macOS.

If you do have apps installed or documents you need, use Disk Utility to create a backup or two on an external scratch device, then wipe the disk and reinstall macOS and migrate in your data.

The ability to use an Apple ID to recover your login would be handy, but that and most other sequences are tied to knowing your login name.

Depending on which Mac—if yours is new enough and has the T2 security chip, or if you're using an older release of macOS, you can boot into single-user mode—the startup key sequences differ by version, if this Mac is running macOS High Sierra 10.13 or earlier—mount the disk, and and then issue the command ls /Users to see the short names. The path into Terminal is described here: Start up your Mac in single-user mode or verbose mode - Apple Support

Here are the unhelpful-here password-related steps Apple recommends:

Reset your Mac login password - Apple Support