It is common for someone to be known by a nickname. For example, Charles Darwin’s brother Erasmus Alvey Darwin was allegedly known as "Eras".
Enter the nickname on the Naming tab of the Current Person Other Detail dialog (click the ‘…‘ button next to the name fields). The nickname then appears on charts and in reports.
On charts the nickname is shown in quotes, e.g. John Smith "Jack"; each chart has a Nicknames in quotes option to switch it to brackets instead. The mini charts inserted into chapters follow the Nicknames in quotes on mini charts setting on the Reports tab, which is on for new projects.
If Prefer nickname is checked, narrative reports use the nickname in most places, only using the full given name in formal contexts such as chapter headings.
Note — A nickname is usually something other than one of the formal given names, or a shortened variant of one. Someone called John might have a nickname of Jack; Elizabeth might be known as Betty. For people known by a middle name rather than a nickname, see Known by second given name.