The previous Lord of the ThunderCats, Claudus ruled Thundera with a fierce heart and razor claw. During the siege of his capital city he is forced to make the choice of giving up the Sword of Omens in exchange for his friend Panthro. He and Tygra are later rescued from having to make that choice by the timely arrival of Lion-O.
But Panthro stabs King Claudus in the back, then revealing himself to be Mumm-Ra, an ancient nemesis of the ThunderCats, in disguise. As he dies, the last thing Claudus says to Lion-O and Tygra is, "No matter what happens, you made me proud today".
Lion-O and Tygra are then captured along with Jaga and Cheetara. In Episode 3, it is shown that the trio is holding a funeral for Claudus and Lion-O etching the Thundercats symbol on the broken statue of his father.
In "Old Friends," a flashback revealed that both Panthro and Grune fought alongside Claudus in a war. During a training in front of Claudus, of Lion-O and Tygra, Panthro and Grune trained hard to see which of them will be promoted to head general.
Claudus is a true king, both in his bearing and his sheer size. He is of above average height with broad shoulders and massive muscles and wears blue-grey armor similar to his blood-child's. He very much resembles Lion-O, except that Claudus has generally much larger proportions than his son who possesses a much more agile and streamlined build. Claudus also sports a horizontal scar across his nose and a massive red mane much like Grune does. The physical differences between Claudus and Lion-O also seem to reflect how they lead: Claudus with unrelenting power and relying on the past to found his decisions upon, whereas Lion-O leads by faith, mercy and looks to what could be rather than stubbornly sticking to the past.
A proud king and a fierce warrior, Claudus is both an imposing but beloved ruler. He rules with strength and shows no mercy to any of his enemies, whether they truly be enemies or not.
Under Claudus' rule the Cats thrived while all other animals struggle to survive. He shows no mercy to other species when they have committed the slightest infraction towards his people regardless of justification as shown when he captured lizards, put them in stockades and allowed them to be jeered at and beaten when they stole some food to feed their starving families. When Lion-O tried to defend them from being beaten Claudus initially reprimanded him before releasing them. He ultimately realized however that he was letting his own people lower themselves to the level he saw other species at.
He was a stern father and unfortunately a very nepotistic one. He much preferred his adopted son Tygra, openly stating that he wished his blood son Lion-O would be more like his adopted one. He also allowed Tygra to sit next to him during the games while Lion-O sat further away.
He did not approve of Lion-O's interest in technology, nor his not taking his duties as future king seriously or his compassion for animals outside his species. However he did see wisdom when he said they would not have so much trouble with the lizards if they treated them with more compassion rather than treat them as inferiors.
Lion-O was Claudus's biological son. He did not approve of Lion-O's beliefs in technology and would question Lion-O's judgement and duties as prince, always hoping he would be more like Tygra. Sometimes Claudus would openly show his favor of Tygra over Lion-O, but in the end he loved Lion-O very dearly.
Tygra was Claudus's adopted son. He had a very close and affectionate relationship with his adoptive son, and sometimes would wish Lion-O would be more like him. He would even accompany Tygra while studying military Strategy and allow Tygra to sit more closer to him during events.
At the time of Thundera's downfall and Claudus's death, his last words to Lion-O and Tygra were; "No matter what happens, you've made me proud today".
- The Book told that it was the Thundercats, our ancestors, who first defeated Mumm-Ra. It was the Thundercats who brought law and order to a world of warring animals. And it is now the Thundercats who are strong enough to maintain this fragile peace!
- You hold in your hands what built the ThunderCats empire. But only he who is deemed worthy can harness its awesome power.
- Larry Kenney, the original voice of Lion-O in the 1980s series is now the voice of Claudus, the father of Lion-O and Tygra.