He is voiced by Yasunori Masutani in the Japanese version of the anime, and by Brian Hathaway in the English version of the anime.
Like most Celestial Dragons, he sees most people as inferior or below him and other Celestial Dragons. In addition to this sentiment he have about most people, Jalmack feels justified attacking people without warning such as shooting a rocket at Sabo's ship because he thinks it crossed his ship. Jalmack also have a strong dislike for pirates and see them as enemies to the World Government. He lacks empathy for his action and does not mind the fact that he attacked a ship that had a child on it.
Over 10 years ago, Jalmack sets sail to go to Goa Kingdom in East Blue. He is about to meet with the nobles of Goa Kingdom to socialize with them. On the way to the Goa Kingdom, Jalmack's ship came across Sabo's ship (as the child sets off on his own journey). Annoyed at the presence of the ship and how it is too close to his ship, Jalmack launches a rocket at the ship destroying it. Jalmack remarks about the ship having a pirate flag and how it came too close to his ship. After shooting down the ship, Jalmack and his men continues to sail towards Goa Kingdom to meet with the nobles there. Unbeknownst to Jalmack, Sabo did not die from the attack and is saved by the Revolutionary Army, but because of the attack he ends up losing his memories.