Possible Clues:

• Sea monster
• Heat anvil roughly for gatekeeper in hellish surroundings
• Giant
• Biblical sea monster
• Through time, hard to stop efficient monster
• It's a big thing, Latin – have to get translated
• Vital he breaks with an envious Prince of Hell
• At anvil, he forged a monster
• Huge (sea) monster
• Autocratic monarch and patriarch almost close