Answer the following Q with stream of consciousness. Context: During another summer with his Aunt Petunia and Uncle Vernon, Harry Potter and Dudley are attacked by Dementors. After using magic to save Dudley and himself, Harry is expelled from Hogwarts, but the decision is later reversed after a hearing at the Ministry of Magic. Harry is whisked off by a group of wizards including Mad-Eye Moody, Remus Lupin, and several new faces, including Nymphadora Tonks and Kingsley Shacklebolt, to Number 12, Grimmauld Place, the childhood home of his godfather, Sirius Black. The building also serves as the headquarters of the Order of the Phoenix, a secret organisation founded by Albus Dumbledore, informs Harry Potter that the Ministry of Magic is oblivious to Lord Voldemort's return. At the Order's headquarters, Sirius Black, mentions that Voldemort is after an object he did not have during his previous attack.

Question: what was the order of the phoenix in harry potter?
To answer this question, we should know that: The building also serves as the headquarters of the Order of the Phoenix, a secret organisation founded by Albus Dumbledore, informs Harry Potter that the Ministry of Magic is oblivious to Lord Voldemort's return. Therefore, the final answer is a secret organisation founded by Albus Dumbledore.