What is the last name of the person who was interested in getting it from embryonic stage to a song that could be mixed and put on a record?"  Answer the above question based on the context below:  In 2006, U2 started work on the follow-up to How to Dismantle an Atomic Bomb (2004), collaborating with producer Rick Rubin. After U2 guitarist the Edge worked individually with Rubin in Los Angeles, the group spent two weeks in September 2006 completing songs with the producer at Abbey Road Studios in London. Later that year, the band released two songs from these sessions on the compilation album U218 Singles: a cover of the Skids' "The Saints Are Coming" with Green Day, and "Window in the Skies". In January 2007, lead singer Bono said U2 intended to take their next album in a different musical direction from their previous few releases. He said, "We're gonna continue to be a band, but maybe the rock will have to go; maybe the rock has to get a lot harder. But whatever it is, it's not gonna stay where it is."Rubin encouraged a "back to basics" approach and wanted the group to bring finished songs to the studio. This approach conflicted with U2's freeform recording style, by which they improvised material in the studio. The Edge said, "we sort of hadn't really finished the songs. It's typical for us, because it's in the process of recording that we really do our writing." Bassist Adam Clayton said, "once we have a song, we're interested in the atmospherics and the tones and the overdubs and the different stuff you can do with it... things that Rick was not in the slightest bit interested in. He was interested in getting it from embryonic stage to a song that could be mixed and put on a record." They ultimately decided to shelve the material recorded with Rubin, but expressed interest in revisiting it in the future.
The answer to this question is:
Rubin