Is it legal to ask for my information? [closed]

Is it legal for air companies to ask for my personal information?

I mean, today I had to buy a ticket from easy jet. To do so, I was forced to register to the site, choose a password, and to insert some personal information, among which where I live, my telephone number, my real name, and also the purpose of the trip.

All of this info was compulsory and regarding only the account that I was about to create.

Can they do this? And can I just ignore them and put on fake information? I realise I have to write my real name when it asks me who is going to travel, but when it comes to registering on their site, I can write whatever I want or not?