Sample cast list from the Folly Theatre, London, Feb. 7, 1880. We index all names.
The Johnson online catalogue and the ProQuest project: The John Johnson Collection: an archive of printed ephemera are rich sources of names. If you know that your ancestor was a tradesman, a performer, an artist, engraver, lithographer, author etc etc try our Names indexes.
In the Johnson online catalogue, Browse the names index (better than searching as the Christian name may have different forms, or be represented only by an initial). Names are differentiated by diphs, e.g. [author], [criminal] which help you identify the correct person. Use the "Expand index" button to give you the genre of the item and its date (where known).
In the ProQuest project, use the Search screen (you can limit this to Booktrade, Entertainment, Popular Prints, Advertising or Crime). You can use drop down lists to identify the name you want and you can limit by role. Click on the blue link in the record to get the full record. You can also search in the quick search box for uninverted names (e.g. Conan Doyle). This will search the full text as well as the catalogue records and will give you hit-highlighting within the record and image(s).
Use the full bibliographic record to discover addresses, etc.