Zach parents died in a car accident when he was young. He was raised by his Uncle, Neil, and his elder brother, Ed in California. He attended the same high school and then University with Laura Andrews.
He is generally a cheerful guy. He has an active scientific and naturally curious instinct from being a Physics Major at University. He will often make jokes in dangerous situations as a way of dealing with fear. He also hates the cold.
Zach was attending the University of California when he, along with Laura Andrews, crossed paths with The Doctor multiple times before together they faced off against the Isopti Queen beneath the University Library. With The Doctor he has encountered The Krillitanes and The Cybermen
Zach had been in love with Laura for a long time before they even met The Doctor. He finally kissed her in the Series Two story "The Labryinth Hotel" after which she revealed that she'd always known and was waiting for him to be ready.