The main originator of systematic desensitisation was Joseph Wolpe (1915-1997), he was born in South Africa and worked as a psychiatrist in South Africa, the UK and US, ending his career at Temple University, Philadelphia.
When working as a medical officer in the army he came to see that alternatives to psychoanalytical psychotherapy were needed. His work played a major part in new psychological treatments which have now helped millions around the world.
There is a great documentary covering his life and the psychological theories and treatments he helped develop available at BBC Radio 4. There are also interviews with people who have undergone treatment and how it helped.