The Lord of Calamity (災禍の顕主 Saika no Kenshu?, "Lord of Destruction") is a figure which appears in the storyline events of Tales of Berseria and Tales of Zestiria. One such being acquired his power due to a curse of immortality which caused him to accumulate far more grief, despair and negative emotions than most humans are capable of in their lifetimes; however it is known that there were other Lords of Calamity in the distant past, and so other means to achieve the power may exist. It is implied that a powerful enough Shepherd could take the Lord of Calamity's place, and being able to form a contract with a dragon—in the same way the Shepherd forms contract with his seraphim prime-lords and sub-lords may be a requirement.
Tales of Zestiria
The Lord of Calamity of Tales of Zestiria is Heldalf. He was cursed with immortality and misfortune by the previous Shepherd called Michel, who sacrificed his baby nephew, Mikleo, on an altar to the Five Great Lords leader Seraph Maotelus. The curse also brought death to all those close to Heldalf, including his newborn son, who was seemingly transforming into a hellion before being put down by Heldalf.
Heldalf only realized his true form as the Lord of Calamity when he attempted to commit suicide by throwing himself onto an active battlefield. Unable to be struck down, the surplus of negativity on the battlefield empowered him into his current lion-like form, though it is not known how many Lord of Calamities there have been. Heldalf mentioned to Sorey during their final battle that once a new Shepherd arrives, a new Lord of Calamity is born, meaning that it is destiny that the two powerful figures fight against each other.
Tales of Berseria
In Tales of Berseria, Velvet Crowe was referred to as the "Lord of Calamity" by the members of The Abbey, who widespread the term to their battle platoon of exorcists and to the Wasteland world during that time. The term was founded by Artorius Collbrande, a saviour who became a Shepherd through unknown means. This is where the lore began of having a Shepherd always fight against a Lord of Calamity—in the distant future, being passed on through folktales of the old and stating that the first Shepherd was a hero and that the first Lord of Calamity slayed beings from all over the world; whereas in fact, it was completely the opposite.