How to retrieve my iMac hard drive password

Reset Computer Password 

Intel Computer

1 - Restart computer and immediately hold Command + r keys

2 - Top Tool Bar >> Utilities >> Terminal

3 - Type resetpassword as one word and no spaces

4 - Press Return key

5 - Follow the prompts and remember the New Password

BUT, if the computer has a Firmware Password that is different and Only Apple can unlock the drive if you have the Original Documentation of Proof of Purchase

Try this guide: https://support.apple.com/en-us/HT202860

Welcome and thank you too :-)