For nearly seven decades, painter Don Bachardy has lured Hollywood luminaries — from Marlene Dietrich to Mark Ruffalo — to sit for portraits, most frequently inside his second-floor studio perched atop a converted garage at his cliffside bungalow overlooking Santa Monica Canyon. There are now 17,000 Bachardy portraits in existence, some of which have landed at the Smithsonian, the Metropolitan Museum of Art and the National Portrait Gallery of London. More than 100 — from his early, tightly constructed black-and-white watercolors to his more expressionistic latter-day portraits, including decades of self-portraits and paintings of his partner of three decades, the novelist and playwright Christopher Isherwood — will go on display April 12 (through August) as part of “Don Bachardy: A Life in Portraits” at the Huntington Library, which will soon be the recipient of the artist’s vast archive, perhaps the most definitive fine art rendition of Tinseltown in history.

“Don and his brother would go crash...