Aside from his great friend and co-star Sir Ian McKellen, few actors could compete with Sir Patrick Stewart when it came to gravitas. Trained classically with the Royal Shakespeare Company and with decades of theatrical experience behind him, he brought legitimacy to Fox's X-Men universe in an extraordinary performance as Charles Xavier. And he, of course, reinvented Star Trek as the heart of the next generation, Captain Jean-Luc Picard. Both of those roles used Stewart's presence on screen to make the X-Men's leader and the captain of the USS Enterprise figures of fierce dignity. They became pop culture icons and...