AccountName[SystemName returns the account name of the SID on the computer given in SystemName. For more information see the see also section. EJwsclWinCallFailedException if the call to a winapi function failed

If the compiler directive JWSCL_SIDCACHE or JWSCL_USE_CACHES is active GetAccountSidString uses an caching algorithm per thread basis to return the name. A new SID is stored in the global JwSidNameCache variable (per thread) and used every time the same SID is returned. A SID is determined by its SidString (property) and its System name. 

COM: Also available as com method.

TJwSecurityId Properties