His primary motivation was his desire to recapture his psychic daughter, Elmira, who's powers he intended to use to further the Spung Empire. Over the course of the show, he also developed a personal hatred for the main heroes and would go out of his way to destroy them as well.
He was portrayed in the series by George Takei, who is most famous for his role as Officer Sulu on Star Trek.
Little is known of his history before the show. According to Commander Goddard and Elmira, he is famous throughout the galaxy for being a ruthless military leader and fond of torture. As he has a daughter, he probably was once married and had a family, but the status of his wife, or any other children, is never revealed. It is also implied by Commander Goddard that he and Shank had met on the battlefield during the Spung-Andromedan war, but no specifics are ever given.
At the beginning of the show, he primarily seems to be a space pirate, raiding ships that venture beyond the Sol System and U.P.P. (United Populated Planets) space. The crew of the Christa first encounter him after taking his daughter, Elmira aboard. Elmira says she was fleeing from Shank, who would torture her and experiment on her to convince her to use her powers for him. The Christa was able to escape through a white hole while Elmira fired on her father's ship to distract him.
They would next meet Warlord Shank in the first season finale "On The Road To Find Out", when the Christa came across another Lumanian built ship that had been badly damaged. Going on board to find survivors or supplies, they find Warlord Shank. It turns out Shank's warship, the K'zata, had found this ship and attacked it, believing it to be the Christa. However, the other ship was able to overpower and destroy the K'zata, but not before Shank was able to escape in a pod and landed on board.
Wanting to learn about the power of this ship, Shank captured and interrogated most of the landing party (consisting of Catalina, Harlan and Radu). However, as they didn't know anything about the ship either, Harlan fed him a lot of technobabble that Shank is too proud to admit he does not understand. During the interrogation, the crew also learns that Elmira is on board. She had been recaptured by her father, who had taken her into the pod with him. Eventually, Bova is able to overpower Shank and they all escape back to the Christa. However, as they are getting back on board the Christa, Warlord Shank grabbed Catalina and pulled her back in, just as The Christa takes off. The self-destruct on the other ship (which the Lumanians had set before leaving as a "surprise gift" to Warlord Shank) goes off, seeming to take Shank and Catalina with it.
It is later revealed that both survived, Catalina was saved at the last minute by an inter-dimensional being named Suzee who swapped places with her, forcing Catalina into her dimension, while she took her place aboard the Christa. Warlord Shank also managed to escape, although the details of how are never fully given.
The last appearance of Shank came in the series finale, "A Friend in Need". The crew of the Christa come across a sentient space station that holds Suzee captive, hoping to make Suzee its friend. While they try and rescue her, the computer reads their minds and learns about Warlord Shank, creating a hologram of him to scare the other kids away.
The crew learns of the deceit just in time for the real Shank to arrive, seeking revenge for his lost crew and ship (which he blame the Christa for). The station knocks out his weapons systems, making it impossible for his to fire from his ship, so he takes a landing party to attack the crew on the station. The crew initially thinks he's a hologram and taunt him, only to learn he is the real Shank and flee. Shank pursues them for a while, but Suzee is eventually able to reason with the station, which lets them go, while keeping Shank trapped. The Christa leaves, stranding Warlord Shank aboard the station.
Warlord Shank is shown throughout the series to be volatile and quick to anger, but also clever and cunning. He is shown to use tricks and traps in many situations that he can overpower his opponent in (such as using darts to capture the crew in "On The Road To Find Out"). Unlike other Spung, Shank does not appear to follow any particular warrior code or honor system, doing whatever he feels necessary to achieve his goals.
While he clearly has a family (mainly Elmira) he never shows sympathy or care for them, treating his daughter as a means to an end and not a person. It is heavily implied that he has used torture on his daughter to try and convince her to use her powers for him, and shows frustration at her disobedience, without any sign of understanding or care.