First Great Western has officially launched its new brand, Great Western Railway, returning to its roots.
The rail company said it was hoping to "rediscover the pioneering spirit" of the old name and service that first operated the line.
Managing director Mark Hopwood said the rebrand was a "historic milestone".
"It is the perfect opportunity to launch the Great Western Railway once again," said Mr Hopwood.
"It's a new dawn for our railway and we're excited to be at the helm."
Great Western Railway has so far said that there are no plans to increase rail fares in order to offset the cost of the £7.5 billion rebrand. But there have already been disputes with trade unions.
The Rail, Maritime & Transport (RMT) union is concerned that changes to the trains will result in guards and on-board catering being scrapped.
GWR unveiled three new trains today (Monday), complete with a new green colour and new logo. It is estimated that it will take until at least 2018 for all of its trains to be rebranded.
Tim O'Toole, chief executive of FirstGroup, the operator of GWR, said: "The franchise will see new or refurbished trains on every part of the network, resulting in more frequent and faster journeys and an increase in the number of seats, keeping people moving and communities prospering."