Liam's answer is spot-on, but I would like to add some details.
"Dawn wall" is actually not the name of a route, but of a portion of the south-east face of El Capitan, which you can see in the figure below:
Figure: the south-east face of El Cap. From www.xRez.com
The first ascension of El Cap passing through the Dawn Wall was realized in 1970 by Warren Harding and Dean Caldwell after 27 days on the wall (source). The name given to this route was Wall of the Early Morning Light (WEML).
Since then, other routes have been established on the Dawn Wall, most notably (source):
Mescalito VI 5.7 C3F or A2 (FA:October 1973. Charlie Porter, Hugh Burton, Steve Sutton)
New Dawn VI 5.7 A3 (FA:June 1972. Charlie Porter)
Caldwell and Jorgeson's route is called Free Dawn and it resulted from the combination of 14 pitches of Mescalito, 2 pitches of Adrift, 4-5 of WEML, 2 pitches of Tempest and 8 new pitches (source).
What is remarkable about their ascent, apart from the very remarkable fact that it was a free ascent, is the amount of time and work that they had to put into finding a path that would allow for the route to be free climbed.
It was not a "mere" free ascent of a pre-existing aid route, even if some people seem to think that what Tommy and Kevin did was "just" a free ascent of the old WEML route.
In total, this super-project took 8 years (from 2007 to 2015), and a lot of this time was spent just looking for a viable route.