For portraits it takes more than 1 lens because there are so many different types of portraits.
One person or multiple people, head shot, head & shoulders, 3/4, full body, in studio, environmental, etc.
When I was still making portraits for a living I had 14 lenses, though a lot of those didn't get used very often.
Like John my favorite portrait lens for 1 or 2 people was a 200 mm f/2 prime lens, with my 135 mm DC f/2 prime second and my 105 mm DC f/2 prime 3rd. For large groups shot outside I usually used a 300 mm f/2.8 prime.
DC stands for Defocus Control, a Nikon feature that lets the photographer selectively soften (defocus) elements in the background or foreground.