Diana Meachum is a lawyer who defended Thomas Roan in his DUI (Driving Under Influence) case.
She has a son named Brian Meachum.
She "convinced" Thomas to take a deal which ultimately put him in prison for eighteen months. Unfortunately, Thomas was later stabbed and killed in a mess hall fight in prison ten days prior to the events in Loa Aloha (episode). His father, Travis Roan, driven insane by grief and rage against those responsible for his son's imprisoned targeted Meachum, having already carried out a series of revenge killings against the prosecutor and the judge who tried Thomas.
Luckily, Lieutenant Commander Steve McGarrett managed to get a warning to Diana which she got and as she and her son fled, Steve and his partner, Detective Danny Williams swept in and arrested Travis.