Who Is Marcus Brooks on 'This Is Us'? What's His Connection With the Pearsons?

Spoiler alert: This article contains spoilers for Season 6, Episode 17 of This Is Us.

Season 6, Episode 17 of This Is Us, the penultimate episode of Dan Fogelman's beloved family drama, celebrates the circle of life by showing the stories of the tragic death of Rebecca, the Pearson family matriarch, and a rare scientific breakthrough achieved by Dr. Marcus Brooks, the Alzheimer's disease researcher who was a boy in the same hospital as Jack Pearson the night he died.

Two actors made their debut on This Is Us in Season 6, Episode 17. Jonigan Booth joins the show as the younger version of Marcus, the boy who was in the hospital the same night Jack Pearson died. Luke Forbes plays the older version of Marcus (aka Dr. Marcus Brooks), who is ready to earn renown as a pioneering scientist.

Jack and Marcus are in the same ward when Marcus is a boy. Marcus's family is anxiously awaiting further updates concerning the boy's injuries. It's during this time that Jack passes on the Pearson family words of wisdom first imparted to him by Dr. K. (Gerald McRaney), to Marcus's dad, Kenny (Dulé Hill).

"You took the sourest lemon that life has to offer and turned it into something resembling lemonade," Jack tells Marcus's dad. In the present day, Dr. Marcus Brooks continues to rely on the quote — using it as a source of motivation went the going gets tough.

Now a scientist researching Alzheimer's disease, Dr. Marcus Brooks is shown as someone considering giving up because he failed to secure funding for a project. Later in the episode, he achieves a breakthrough — devising the treatment for patients like Rebecca Pearson.

Season 6, Episode 17 of This Is Us uses a train metaphor to show Rebecca's death. Buckle up, this is where we enter tearing-up territory. With Kate (Chrissy Metz) away in London on business, the family remains on standby as Rebecca's condition worsens overnight.

Led by Beth (Susan Kelechi Watson), the Pearsons line up to say their goodbyes. Kate arrives in the morning, just in time to see her mom one last time. With William (Ron Cephas Jones) as her guide, we see a young Rebecca walk through the train, reuniting with Jack (Milo Ventimiglia) once she reaches the caboose.

"I always thought that the second-to-last episode would end with Rebecca's death. As we did," Dan Fogelman told Deadline. "In the last episode, we will try to capture something simple which, while sad, is kind of a day in the life, which is so much of what the show is about, set against Rebecca's funeral."

Season 6, Episode 17 relies on a genius editing trick, interspersing Deja's scenes with those of Dr. Marcus Brooks. Early on, Deja describes her man as a workaholic, before the scene cuts to Marcus working late in his lab — suggesting that she and Dr. Marcus Brooks might be an item.

Later we learn that Deja reunited with her childhood sweetheart, Malik (Asante Blackk), and that they're expecting a baby. As Deja tells her dad, she's anxious about the timing because the pregnancy coincides with the beginning of her medical residency.

The Season 6 finale of This Is Us airs on Tuesday, May 24, 2022, at 9 p.m. EST on NBC.