GoDaddy.com

GoDaddy, like Register.com, started it's life as another company.  Eventually they changed their name and became the largest domain registrar in the world.  They had over 25 million domain names under management by 2010.  We all know them for their famous Superbowl commercials.

Register.com Registrar

Originally there were 5 domain registrars that tested the new domain registration system.  Register.com was one of the original testers and are still around today registering domains.  It all began in 1999 and in 2000 they went public.