Like King Triton, he believes humans are dangerous because Merroway Cove was once attacked by humans; many merfolk were hurt, including him evident by the scar on his left arm. He is the chief adviser of Queen Emmaline, and vehemently advises she wields her trident as a weapon against any human vessels that come to Merroway Cove.
Plank is an extreme misanthrope. Due to the attack that gave him his scar, he fears humans to the point where he's always inclined to belive the worst of them as shown when he says "We can't trust any humans!" and when he accused the Royal Family of Enchancia of taking Princess Oona despite there being evidence against it. He is shown to especially dislike humans who have magical abilities such as Princess Sofia as shown when he began talking about Sofia as though she weren't there even when she was in his presence and refered to her as "the girl" and refused to believe her claims about Oona being abducted by a sea monster until the latter was rescued despite mounting evidence that proved she was telling the truth. He also had a habit of interupting people.
Role in the Series
He first appears along with Queen Emmaline after Sofia follows Oona and Cora home. When Oona and Emmalne have a dispute about the Floating Palace's presence in the cove, He sides with Emmaline prompting Sofia to swim forward and side with Oona, revealing herself. Emmaline and Plank both tell Cora, Oona, and Sofia about how he got the scar on his arm. Sofia tries to assure the pair that the humans on the ship mean no harm but they don't take her seriously both because they can tell she's a child and because they think she's a mermaid. He urges Queen Emmaline to use her trident to conjure a storm to move the ship out of the cove but Emmaline, Sven, Sofia and Oona, are all against the plan because that might sink the ship. Sofia proposes a more peaceful solution: She'll go up and convince them to move the ship. When Plank and Emmaline both ask her how she would do that, Sofia reveals that she's really a human and that the ship belongs to her family. Plank instantly starts acting negatively toward her prompting Oona to swim forward and angrily silence him. Emmaline commands Sofia to do that and never come back.
When Sofia comes back and tells the colony about Oona's abduction by a sea monster, he refuses to believe her because of his hatred of humans and accuses her family of taking Oona captive and sending "the girl back to lie to us." Emmaline gives her until sundown to return her daughter or she'll sink the Floating Palace. Plank follows Sofia to keep an eye on her and sees her go up to her ship but is surprised when she comes back without Oona and wonders where she's going. When time's up, Emmaline uses her trident to conjure a storm to sink the ship.
Sven, who had gone with Sofia and saw the monster with his own eyes, stops her before the storm gets too fierce and leads her and Plank to Oona, who tells them they have Sofia to thank for the fact she's safe and Cora tells Plank off. Emmaline uses her trident to stop the storm. Plank abandons his hatred for humans and becomes friends with Sofia's family.