Quite frankly – this is the coolest named tool out there: John the Ripper.
Often you’ll see it abbreviated as ‘JTR’ this is an awesome bit of hacking software that is designed to crack even very complicated passwords.
John the Ripper, mostly just referred to as simply, ‘John’ is a popular password cracking pentesting tool that is most commonly used to perform dictionary attacks. John the Ripper takes text string samples (from a text file, referred to as a ‘wordlist’, containing popular and complex words found in a dictionary or real passwords cracked before), encrypting it in the same way as the password being cracked (including both the encryption algorithm and key), and comparing the output to the encrypted string. This tool can also be used to perform a variety of alterations to dictionary attacks.
If you are somewhat confused between John the Ripper and THC Hydra then think of John the Ripper as an ‘offline’ password cracker whilst THC Hydra is an “online” cracker. Simple.