Why is there a "had been" in this sentence - English grammar question.?

[Firstname]

"I realized that social media would be transformational for businesses and decided to start a software company that would help Fortune 500 companies manage their marketing efforts using social media. Steve Garrity, who 【had been】 a computer lab partner of mine at Stanford, left his job at Microsoft to start that company, Hearsay Social, with me in 2009."
If I substitute "was" for "had been" then what's the meaning of the sentence and what's the difference between the sentence with "had been" and with "was"? Thanks in advance!
SirGeorg..., do you mean if I substitute "had been" for "was", it will be wrong because people who read the sentence will think that when he was my partner and working at Microsoft, he left school and the job to start a company with me?

[justme]

Basically they both mean the same ting with only a tiny nuance in them "Had been" is just a little more definitive. Substituting "was" will make no difference to the sense of the sentence.

[Deviant]

'Was' sounds a lot more natural and I would recommend changing it to that, however I think 'had been' also works.
It's quite a subtle difference and I'm sure they'll be someone who can explain it better but using 'had been' you can talk about a past event while you are already talking about the past, so I suppose it does work here as you are talking about Steve Garrity left his job in the past, while also saying you were at Stanford with him.

Hope that helps, sorry about the unclear answer - hopefully you get a clearer one!

[SirGeorges]

"Had been" is past perfect, "was" is past simple.

Steve, who HAD BEEN my partner, LEFT.
...................far past.......................past

It's like "By the time I arrived(past simple) everyone had already left(past perfect)"
It shows a sequence of things, if you used past simple ("was") it would still make sense but that sequence of things would be lost, it would mean that while he was your partner at Stanford he left to start a company with you, whilst if you used past perfect("had been") it would mean that he firstly used to work at Stanford, and after his work there was over, he joined you to form another company.

[Goddess of Grammar]

Steve Garrity's CV goes like this

(sometime long before 2009)--student at Stanford and lab partner of "I"

(sometime before 2009 until 2009) worked at Microsoft

2009--started Hearsay Social with "I"

If you replaced "had been" with "was", it wouldn't be wrong, but it wouldn't be clear that Stanford was before Microsoft.