What is Dr.who user. 100s of yarn jobs are getting triggered with Dr.who in my cluster.

[#1]

Hundreds of Yarn jobs are triggered by dr.who user. These jobs go into "ACCEPTED" state and then to "FAILED". 

What is making these jobs to get launched ?

[#2]

The username "dr.who" is the default identity of anyone connecting to HDFS
or YARN via the web server (REST) APIs in an unsecured, non-kerberos
cluster where a connecting user's identity cannot be authentically
determined.

If your cluster is exposed to the internet, and/or you are unable to
recognize any of these jobs, I'd recommend shutting down the service
immediately and investigating a possible external attack. I'd also strongly
recommend following:
https://blog.cloudera.com/blog/2017/01/how-to-secure-internet-exposed-apache-hadoop/
and securing your cluster in such a deployment.