Motherwell's lengthy Wikipedia entry is here, and further information on the Museum of Modern Art web site is here.
If Motherwell ever made representational paintings, I couldn't find any while poking around the Internet. Everything I saw was abstract, which might be explained in part by the fact that he was amongst the youngest of the New York School crowd, not spending the 1930s painting Social Realist scenes like Jackson Pollock and some of the others.
Much of Motherwell's art was political. I think political art is the dregs of art, but in Motherwell's case this didn't really matter. That's because most of those political paintings could have been given entirely unrelated titles and viewers would not have known the difference because nothing representational could be seen.
Below are a few early Motherwells along with some later works.
Part painting and part collage.
Done in colored inks. This is about as close to a figurative work as I could find. Not sure if this has to do with Motherwell's obsession with the 1936-39 Spanish Civil War or some aspect of World War 2, which was raging at the time he did this.
Part of a series related to the breakup of one of his marriages.