Is eliyahu hanuvy real? is he really coming by shfoch chamoschu or it's just the Jewish version of Santa Claus?
Eliyahu Hanavi was certainly a real person, and is mentioned in Tanach a number of times. See his Wikipedia page for more details.
There appear to be a number of reasons why the door is opened at this point in the Seder, and many of them are unrelated to Eliyahu Hanavi. See the answer to my question here. Certainly there is no need to believe that the door is opened (or that the extra cup is poured) for Eliyahu to physically enter (and drink).
(There are some who do believe/understand that Eliyahu Hanavi appears at the Seder in some spiritual form (see here). While there are certainly some elements of similarity to "Santa", there is probably Kabbalah/Jewish mysticism behind this that I do not understand, and I would not lightly discard it without understanding th entire background first.)
My grandfather related from his father this explanation (a somewhat similar explanation is given in Taamei Minhagim) In past times Jews frequently suffered from blood libels in which it was alleged that they used the blood of a Christian boy for the wine at the Passoer Seder. When the gentile police (or mob) would show up at the door demanding to taste the wine, the children would be understandably scared. The parents would comfort the children by telling them "Don't worry zeiskeit, its Eliyahu Hanavi".
Taken from the following link: Eliyahu Hanavi
Few nevi'im (prophets) are as well known as Eliyahu HaNavi. He is a figure not only of the past, but also of the present and future.
Even after ascending to heaven, he continues to advocate on behalf of his nation. A seat of honor is set for him at every bris milah and a cup named for him is poured at the Seder. He will be Hashem's messenger to herald the coming of Mashiach.
All this is true, but it is not nearly a complete picture of the prophet whose exploits are spread over seven chapters of the Book of Kings. With incredible courage he opposed the evil King Achav and his villainous Queen Izevel. Achav flooded the Ten Tribes of Israel with Idolatry and Izevel ordered the slaughter of every prophet of Hashem, and would have done the same to Eliyahu had Hashem not carried him to safety. Though Eliyahu sharply admonished Israel for its sins, his love for them was as great as his anger, and he helped them whenever he could. In one of the most inspiring episodes in all of Tanach, Eliyahu brought hundreds of thousands of Jews to Mount Carmel and proved to them that the prophets of Baal were charlatans. United, the entire multitude proclaimed, "Hashem - He is the G-d! Hashem - He is the G-d!"
Finally, when Eliyahu's mission on earth was complete, Hashem took him up to heaven in a whirlwind. Who was Eliyahu? How can we understand his zealotry? What was his mission? How was he unique? What is his legacy for us? The Sages in the Talmud and Midrashim, the commentators on Tanach, and the classic Torah works are filled with descriptions and discussions about Eliyahu.
In this magnificent volume Avrohom Yom Tov (Abie) Rotenberg scours the classic literature to bring us an unprecedented picture of Eliyahu and his mission. Rabbi Rotenberg cites the verses in Tanach and explains them. And he delves deeper and broadens the portrait based on the major commentators.
Nowhere is there such a complete picture of the prophet and an analysis of his words, deeds, and period. To read this beautiful and profound volume is to informed, inspired, and uplifted.