When the first ads were run in mid 90s when internet was still evolving, they were directly hosted on the web server and placed directly on the website. This is how the era of digital advertising started. Then internet started growing and so did the usage of computers. To host the creatives directly on to the website started becoming more pain for the website owners (publishers) and advertisers had to do a lot of manual reporting and also had to place a lot of trust on publishers with numbers that were reported back to them.
At this time ad servers were invented where their primary purpose was to serve ads. Initially the ad servers invented were only for the publishers to serve ads on their website and do granular targeting of the ads on the sites and not having to go and mess around everytime on the website when there was a new campaign to be delivered. Ad servers allowed them to just have the integration done once and then deliver ads on the site through the ad servers.
Since the use of ad servers started growing and the complexity of the advertising ecosystem started growing, the need to have specialist resources to work on ad servers started growing. Apart from just serving ads, these ad servers now been used by ad networks, ad exchanges, agencies, publishers started providing other features like retargeting, cookie targeting, geo targeting and other key features.
This is when ad operations team started coming into operations where in their main role was to manage how the ads run, they were running the day to day operations of the ads on the ad server working closely with the account management team. This was a short intro on ad operations.
I will right more in detail about how different each ad operations roles are for each of the org.