"I've only known him to be a gentleman who cares first and most for his family," the series' creator Aaron Sorkin tells PEOPLE.
In an e-mail, Sorkin, 46, said, "I've worked with Rob twice – for three years on The West Wing and for another six months when he starred in the [London] West End revival of A Few Good Men."
For the first four seasons of the NBC political drama, from 1999 to 2006, Lowe played deputy communications director Sam Seaborn.
Referring to Lowe's 1988 sex tape scandal, before the actor became sober 18 years ago, Sorkin added: "Rob's had public scrapes in the past, and he's always landed on his feet. I'm sure his energy right now – and Sheryl's – is in protecting his kids."
The Lowes have two sons: Matthew, 14, and John Owen, 12.
Fellow actor Dulé Hill, who has known Lowe for eight years, tells PEOPLE, "I've known him strictly as a family man. What comes first is his children and his wife. That's always been his focus."
Of the current scandal, "It doesn't seem like the Rob I know. It doesn't add up," says Hill, 32. "I'm saddened by what I see and hear. I trust that it will work out."
Reporting by ALEXIS CHIU
For more on the case, including interviews with Gibson's family plus Lowe's friends and former employees, pick up the latest PEOPLE, on newsstands Friday