The site is historic, having served as the London terminus of the GWR and its successors since 1838. Much of the current mainline station dates from 1854 and was designed by Isambard Kingdom Brunel. The site was first served by Underground trains in 1863, as the original western terminus of the Metropolitan Line, the world's first underground railway.
The station is the terminus for services from the west, Tteamslink, and the heathrow express as well as for various inner- and outer-suburban services.
The TfL page is 
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