The Dutchman has also hit out at the critics who he claims have made a 'devil' out of him after just one defeat in charge of the side.
United's 2-1 home loss to Swansea was the shock result on the opening weekend of the Premier League season but Van Gaal is appealing for patience ahead of the trip to Sunderland on Sunday.
"Two weeks ago I was the king of Manchester and now I am the devil of Manchester," he said. "It's the football world and it is especially the media in this football world."
And the former Netherlands coach is calling on the club's supporters, owners and chief executive to join him 'for the long haul'.
He said: "I think the fans of Manchester are intelligent. I've already said that it shall be difficult in the first three months, for the players and also for the fans. I've said it to Ed Woodward and the Glazers that this is what it is.
"They have hired me for my philosophy, not because I'm a nice guy. I am a nice guy but that's not why I was brought here.
"I'm not hired to be fired. I'm hired to build up a team. That process needs time. I bring another philosophy in the club.
"You have to believe in the philosophy that again we make a big club but it needs time. It is not an overnight job."
Meanwhile, Van Gaal refused to confirm or deny speculation that England striker Danny Welbeck has been told he can leave Old Trafford before the transfer window closes.
"The media were not in the room and I do not speak about that because that's private," he said.
"I know what I said to Danny and Danny knows exactly what I said to him.
"I assume that Danny Welbeck is not saying anything about our conversation and also in that conversation was (assistant manager) Ryan Giggs and he doesn't say (anything) either, and that is the way it should be."