Question:  Leonard "Len" Benker Johnson organized a concert and a rally featuring an American bass singer who became involved with what?
Sentence (from "Len Johnson (boxer)"): Leonard "Len" Benker Johnson (22 October 1902 – 28 September 1974 (aged 71)) born in Clayton, Manchester was an English professional middle/light heavyweight boxer of the 1920s, and 1930s, who won the Australian version of the British Empire middleweight title in 1926.
Relevant evidence: Yes