Alvida is first shown as Luffy's first defeated pirate captain. She is very fat and has curly black hair. She also as an over-inflated ego about her looks. You could say she's in denial about how ugly she is. She carries a iron club around, and shows no mercy to anyone who dares to make a bad comment about her looks.
When Luffy entered a ship that was under attack from Alvida's Pirates, he befriended poor Coby. Alvida forced Coby as her swabby after he got on her ship by accident. When Alvida attacked Luffy she was defeated with one blow and was sent flying.
That isn't the last time Alvida is seen, though. The next time is rather strange and odd. Alvida was never defeated by a man before and developed a crush on Luffy. She decided to hunt Luffy down with the power of the Slipslip Fruit or Smooth Fruit, a Devils Fruit that slimed her down. Not only that but nearly everything you throw at her bounces right off, and if she were to take her sandals off she would slide all over the floor.
After taking the fruit, she contacted Buggy, who was defeated by Luffy as well, and they agreed to an alliance. After some searching, Alvida and Buggy met with Luffy in Rogue Town where they were nearly defeated by the Navy. Only by theintervention of an unknown pirate who was wanted for the last 20 years saved both of them.
She follows Luffy and his crew into the Grand Line, searching for the man she loves: Luffy.