Ludwig's Father, the King is mostly a comic relief due to his arguments with his son Ludwig and his fear of his dear wife, queen Almaberga. He is very, very terrified of his wife. She loves to tease(torture) him. In fact he was so afraid of his wife, the spell that was cast upon him broke because of his terror.
He is the elder of the Geltic tribe The Elder believed that it was his son who had created the secret society of Geltic descendants and who was after the treasure but it was in fact Jean Pierre, his professor who had killed him. When Jean Pierre is holding Lara hostage and attempts to flee, The Elder shoots him in his "T" zone.
Merry is Kaya's loyal servant, and was the one who designed the Going Merry. (Source: One Piece Wiki)
Tom was a powerful long-horned cowfish Fishman, known as the most skilled shipwright in the world. He was also the teacher of Iceburg and Franky. (Source: One Piece Wiki)
Curly Dadan is a friend of Monkey D. Garp's and the foster mother of Portgas D. Ace and Luffy. Garp entrusted her to take care of Portgas D. Ace shortly after the boy's birth. Later, Garp also left Luffy in Dadan's care. Dadan lives on Mt. Corvo near the Windmill Village. She is the Mt. Corvo mountain bandit boss of the Dadan family and a wanted criminal. She was first mentioned after the Enies Lobby incident when Garp come to Water 7, which he claims that he left Luffy and Ace to train with a friend. Her name was first mentioned by mayor Woop Slap after he saw Luffy new bounty and questioned "Does Dadan know!?". (source: onepiece.wikia)
Gold Roger (real name later revealed to be Gol D. Roger) was the Pirate King, the strongest pirate alive, and owner of the legendary treasure known as One Piece. Born in Loguetown, Roger was famed as the man who did what no one thought possible — he conquered the Grand Line. Even before setting out, he was the only man who truly did not fear the dangers of the Grand Line and was even excited about venturing out there. Even with warnings about ships never returning from that ocean, he did not care; in fact, he even declared that was the reason for him going. He was said to be completely fearless, and those who witnessed his execution even claim that he grinned just before his death. Many people who've met Monkey D. Luffy and knew Roger have commented that the two are very similar.