Knowledge is the most important characteristic your speakers should possess! And while that sounds like a given, you'd be surprised how many conferences have flopped because their speakers simply didn't know a whole lot about the topic of the conference. Hence, conference organizers must choose speakers with enough knowledge and expertise to deliver a presentation or a speech that your audience finds educating and valuable.
In cases where a celebrity or a public figure is engaged to bring attention to a particular topic or issue, conference organizers must make sure they're well-read and equipped to handle speaking at your event, as well as answering questions from your audience if there are any.
Not only should your speakers have the expertise and a deep knowledge of the topic at hand, they should deliver such content in a charismatic and engaging way so they don't bore your audience into a deep slumber. Not only that, but charismatic and entertaining speakers make your events memorable and enjoyable, guaranteeing a good majority of your audience to attend your next event.
While finding speakers with enough knowledge and charisma is a good place to start, the relevance of your speakers is also key especially if the bulk of your audience is made up of Gen X & Y. Selecting renowned field experts and personalities with ties to your event's subject matter and enough popularity amongst your community guarantees more attendee turnover because people are interested in what they have to say.
All speakers are allowed a degree of novelty in giving their speech or presentation while still reinforcing your conference's key themes and topics because your audience has probably heard it all before, and they came to your event to see and hear something new. Therefore, speakers need to give a fresh take on a topic to keep things interesting.
Resourcefulness entails how your speakers can adapt and handle unanticipated situations like the dreaded, but all too common technical difficulties or controversial questions asked by attendees. A pro tip would be to see your speakers in action before your event to have a better idea about their performance, content delivery and how they handle controversial questions or topics of which conflicting views are present.