He's a star of screens both big and small, but Patrick Dempsey has spent enough time in obscurity to never take the success for granted.

The Grey's Anatomy star might be scorching hot in more than 60 countries now, but if he's as anywhere near as ego-obsessed and as full of himself as some of his TV and movie contemporaries, he's doing a really good job of hiding it.

In almost every interview he's done since Grey's Anatomy became a global hit three years ago, Patrick Dempsey has presented himself as genuinely thankful for the role of stethoscope-swinging sex symbol Dr. Derek "McDreamy" Shepherd.

Before Grey's Anatomy came along, Dempsey was wallowing in mediocrity, and plagued by self-doubt. According to the Melbourne Herald-Sun, he actually kept telling himself, depressingly, "I'm ugly, I'm no good, I'm a has-been."

The actor's spirits flagged when he auditioned for, but barely missed out, on a role in the current FOX hit House. Dempsey was called back as many as 15 times by producers who were divided over his suitability for the role.

Patrick Dempsey tested for the role of Grey's Anatomy's Derek Shepherd only after Rob Lowe (The West Wing, Brothers & Sisters) turned it down.

Dempsey also had to contend with dyslexia when trying to read script pages at audition. He tried to memorize lines because he struggled to read them off the page. He couldn't focus and, at certain times, he could hardly speak.

Patrick was convinced that Grey's Anatomy creator Shonda Rhimes, sitting quietly at the back of the audition room, hated him.

Isaiah Washington was also up for the role of Dr. Shepherd, but Rhimes had no doubt Dempsey was her man. But she was also enamored by the searingly intense Washington and asked him if he'd play Dr. Preston Burke.

Even his detractors concede Washington is a powerhouse performer, but his erratic behaviour threatened to derail the show at its peak success.

Patrick Dempsey remains frustrated there was someone on the set feeding the media information about the scandal that led to Washington's ouster.

He considers the demise of Isaiah Washington a "tragic moment for everyone" that should have been dealt with quietly and in-house.

Asked if he feels relief or sadness about losing Washington as a co-worker following the third season of Grey's Anatomy, Dempsey says:

"There are two things to that. I think the character was phenomenal. It was a great character we've lost, and I think that's a tragedy. And the other stuff? It's much better (Isaiah Washington's exit) in the long run, I think. A lot of lessons had to be learned by everyone and it was tragic."

Patrick Dempsey, a 42-year-old father of three, clearly doesn't have much to complain about. Not only is he loving Grey's Anatomy, he's in strong demand to make films in production breaks from the medical drama.

He's made five movies, including Enchanted and Made of Honor, since Grey's Anatomy took off. So much for critics thinking that being "McDreamy" would mean being pigeonholed and struggling to get work elsewhere.

One of his great challenges, Patrick Dempsey adds with a smile, is maintaining Dr Shepherd's perfect coiffure in and out of bed.

"My sexy bed head ... well, it's an art form in itself. The (hair) product is key, absolutely. And I'm up two hours before my wife (Jillian Fink Dempsey) so it looks great even before she gets up."

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.