Oliver Bargate is a forensic pathologist at the Met and the new boyfriend of Vanessa Ekwensi.¹ Robin is disappointed that she doesn’t get to meet Oliver at her housewarming party, but later gets the opportunity when he agrees, although reluctantly, to provide Strike and Robin some forensic findings in exchange for information that will help Vanessa arrest a local gangster.² Persuaded by Vanessa to meet with them at the Corner Cafe, he appears uneasy during the meeting and relieved when it is over.³

He is described as a handsome black man with a “high rise hairstyle” and “rimless glasses.” ⁴

In Troubled Blood, Robin learns that Vanessa and Oliver are engaged when Vanessa shows up to her 29th birthday celebration with an engagement ring.⁵ 

“‘Might try that bloke your friend Vanessa used to date in forensics, what was his name?’

‘Oliver,’ said Robin, ‘and he’s now her fiancé.’” ⁶ 

^{1: Lethal White, Chapter 39
2-4: Lethal White, Chapter 40
5: Troubled Blood, Chapter 15
6: Troubled Blood, Chapter 39}