When Tumblr founder and CEO David Karp received a query two years ago what he thought about display ads, he said they turn his stomach. Today, he is eating a healthy slice of humble pie as the phenomenally successful blogging platform plans to sell ad display units to advertisers.

Tumblr – Image via Crunchbase

The ads, which will appear on the blogging platform’s dashboard, will be a first for the blogging platform that has so far survived without ads. Showing on the …