Art Levinson is the current Chairman of Apple. He was brought on to the board in 2000 during Job's second act and was present for the introduction of the iPod, iTunes and iPhone.
Art Levinson is always introduced as the former CEO of Genentech but I didn't know his story until I read the Herceptin story in Emperor of All Maladies. Turns out Levinson was trained by Nobel Michael Bishop of oncogene fame. In the late 80's Levinson was leading a group pursuing treatment for breast cancer by doggedly tracking a gene called HER-2. Genentech's executives turned away from cancer research after some high profile failures in the 80's. This should have been the end of genentech's role in HER-2 except for the leadership of Levinson. He dodged the bureaucracy, pursued resources and lead a small team to continue work on HER-2. The group produced Herceptin, one of the most important breakthroughs in chemotherapy in the molecular era in, a jaw-dropping, 3 years.
Reading that story I can see why Jobs would want him on the Apple board.