Eric

Eric the Whirlwind (つむじかぜのエリック Tsumujikaze no Erikku) or sometimes directly subbed as Erik is a mercenary in One Piece. He is a non canon character, appearing in the anime only, being the main antagonist of the Warship Island arc. Here he is hired by Commodore Nelson to capture the famed Thousand-Year Dragon, a creature whose bones are said to be the source of eternal youth. However, Eric was only using Nelson to find the Dragon for himself for its bones, which supposedly would give him invincibility.

Abilities
Eric was skilled enough to be hired by Nelson, and has show to be quite acrobatic, jumping to evade Monkey D. Luffy's attacks. He also seems to be confident of his own abilities, as he is undaunted during his first encounter with the Straw Hat Pirates and does not show any sign of fear upon learning that Luffy is also a Devil Fruit user, which apparently scared the other marines with him at that scenario.

Devil Fruit
Wielding the power of the Kama Kama no Mi, Eric is able to use his lengthened fingernails to cut through the very air to create razor-sharp gusts of varying size. Eric proves himself to be a dangerous opponent when ultimately facing Luffy, inflicting multiple wounds against his opponent, but he proves to be no match for the Straw Hat captain.

History
His part in the storyline is short, but rather humorous. As a mercenary under Nelson's command; he is ordered to retrieve the runaway girl Apis and capture the legendary Sennenryu, Ryuji. He tracks down and follows the Straw Hats throughout the entire Warship Island arc, eventually betraying and (supposedly) killing Nelson and fighting Luffy and his crew in a bid to try to obtain the Sennenryu which will aid him in making the supposedly magical 'elixir'. He manages to deal a significant amount of damage to Luffy, but is defeated when Luffy sends him flying off the Lost Island with his Gomu Gomu no Kane and Gomu Gomu no Bazooka attacks. Eric later reappeared once again to obtain his revenge just as the crew began to climb the Reverse Mountain, leading to the infamous Grand Line, but found himself tipped over the edge of the Going Merry and into the water by the wily thief navigator Nami before a battle could even erupt. He is most likely dead, due to the negative side effect of his Devil Fruit which causes him to be a deadweight in seawater with the strong currents coming from the mountain also put into consideration. He has not appeared in the anime ever since.

Translation and Dub Issues
A running gag throughout that arc was Luffy and the others would mishear the name of his Devil Fruit (Kama Kama) as Okama Okama, making them think Eric was a crossdresser or literally, a transsexual, calling him "Eric the Gay Man" who ate the Okama fruit. In the FUNimation dub, since the name of his Devil Fruit was changed to the "Sickle-Sickle Fruit", the joke was changed to them mishearing the name as the "Sicko-Sicko Fruit".

Trivia

 * This Devil Fruit gives Eric power similar to CP9's Rokushiki move Rankyaku but, as Eric is a filler character, it is unknown which is stronger. Eric's abilities comes from a Devil Fruit power, but the Rokushiki moves are of Super-Human Strength. Luffy was able to withstand Eric's attack with ease, while he recoils after being hit with Rankyaku.
 * In the concept art for Eric, it was shown that he liked to file his nails to keep them sharp.