Human clown performer at the Colosseum of Ashes, an interplanar fighting arena. Has an inflated ego and violent tendencies.

“I am not related to King Taron by blood, but he always treated me as a member of his family. I was a performer at his court, but my true role was to spy on the nobles I entertained. That is my purpose here as well.” - Deathmatch at the Colosseum of Ashes (RPA-SQ1)

Started as a performer in King Taron's court. Ended up at the Colosseum of Ashes.

Kalso displays narcissistic tendencies and hates to be outshone;

You hide behind Kalso as the children throw stones. One hits the clown square in the face. The audience laughs as blood gushes from his nose. Kalso is not amused. Without a word, he slaps the stone-thrower across the face. The other children scatter, fearful of a similar reprisal, and the audience boos Kalso’s maliciousness. He shoots you a furious look. In a huff, he marches from the arena. - Tome of Encounters (RPA-SQ1)

The entry on Kalso in a ledger found in Sylvian's private viewing area further iterates this:

Human entertainer from Ulos. Former court jester and known agent of King Taron from the Kingdom of Nalos. His performances continue to attract large crowds. With an artistic disposition, Kalso requires constant flattery and reassurances. If he refuses to perform, Colosseum administrators should attempt to appeal to his oversized ego before doling out punishment. When a performance fails to meet his expectations, he is a danger to himself and others. - Deathmatch at the Colosseum of Ashes (RPA-SQ1)

Kalso's wooden sword has a retractable blade inside it;

The entertainer flips a small switch at the hilt of the sword. When he does so, the wooden cover detaches, revealing a steel blade underneath. - Deathmatch at the Colosseum of Ashes (RPA-SQ1)