There are several people named Brendan Gregg. This one is me (2011):
In 2018 I was photographed for the Faces Of OpenSource project (thanks Peter Adams).
Conferences often ask for a head shot, so I'll share them here. Here's one from 2017 SREcon, which is also my avatar (thanks LinkedIn):
I previously used my 2013 Velocity conf photo (credit Trav Williams, Broken Banjo Photography):
Others that I used at some point: 2012.
For an amusing older photo, here I am fooling around with data center safety clothing, seated at a text console in 2001:
For another amusing picture, in 2006 I was accused of being a group of clones (due to the volume of software I was writing); so I created this: