The Paclu had four-lobed brains that were difficult for telepaths to read. They, along with the Amoniri, were one of the dominant members of the Breen military due to the fact that they met its performance requirements best. Paclu were generally large and bulky in build and, according to Chot Nar, were very strong. They also possessed multiple hearts. (ST - Typhon Pact novels: Zero Sum Game, Plagues of Night)
The Paclu were native to Pacluro Prime. Their society was divided into clans. Clan Lokaar resided in the frozen north of Pacluro Prime. Until 2386, Herlok Seltran was the scion of Clan Lokaar. (ST - Section 31 novel: Disavowed)
In 2381, the Paclu Thot Keer was in charge of the Typhon Pact's quantum slipstream drive development project. Keer designed the Quantum slipstream drive prototype Marjat at Salavat. He took off his mask before the Marjat was destroyed. Having lived a Breen, he wanted to die a Paclu.
In January 2386, Thot Tran (Herlok Seltran) was in charge of the Breen Confederacy's wormhole generator project. When he defected to the Tzenkethi Coalition, Domo Pran shelved the project. (ST - Section 31 novel: Disavowed)