Sometimes roles are developed keeping an actor in mind and sometimes, an actor lands a role through sheer grit, determination, preparation, and at times, plain, blind luck. Like it happened in these cases: 

1. Anupam Kher - Saaransh

Anupam Kher experienced a fair share of struggle before being cast as a 60+, retired, grieving father Mr. Pradhan in Saaransh - only to lose out on the film almost a fortnight before the shooting was to commence because producers Rajshri Productions insisted on casting an older actor for the role. 

Anupam Kher Saaransh
Source: Janta Ka Reporter

Kher, who was 28 at the time and had prepared for the role for six months, was so dejected by this news that he decided to give up on acting altogether and leave Mumbai. Before leaving, he met director Mahesh Bhatt and gave him an earful, expressing his frustration. That's when Mahesh Bhatt specified to Rajshri that he'd only make the film with Anupam Kher and ultimately, Kher starred in the film.  

Saransh movie
Source: Filmybyte

2. Zeenat Aman - Satyam Shivam Sundaram

Director Raj Kapoor approached various actors for Rupa's role, but most leading heroines of the time, including Vidya Sinha and Hema Malini, rejected it because of the exposure the role demanded. Raj Kapoor did not think Zeenat Aman would fit the role, but she turned up at his office in clothes fit for Rupa's look test, thereby convincing him. 

Zeenat Aman
Source: Tarshi

She went on to win a Filmfare for her performance, and in an interview with The Indian Express, described her experience of convincing Raj Kapoor: 

One fine day I got into the character of Rupa from 'Satyam Shivam Sundaram'. He (Raj Kapoor) was surprised to see me in the look of Rupa (referring to the test look she took). He appreciated my passion towards the character, gave me gold coins, and signed me for the film. 
Zeenat Aman and Shashi Kapoor
Source: The Print

3. James Michael Tyler - F.R.I.E.N.D.S

Tyler immortalized the role of the coffee shop manager Gunther in F.R.I.E.N.D.S, whose one-sided love for Rachel could rival most Bollywood dramas. But, he was actually cast in the role because he was the only applicant who knew how to run a coffee machine. 

Gunther
Source: Radio Times

As Gunther, aka Tyler, shared with Insider, it was a 'lucky accident' indeed: 

I honestly always thought my Masters in fine arts would get me further in the acting world than knowing how to work an espresso machine! That was a happy accident and I'm very, very grateful to have had that skill.
Gunther
Source: Twitter

4. Jennifer Lawrence - Winter's Bone

Lawrence, who was nominated for an Oscar for Winter's Bone, was initially considered to be 'too pretty' for the role by director Debra Granik. That's when Lawrence decided to show Granik she was perfect for the role, by dressing (down) for the part. 

Lawrence in Winter's Bone
Source: YouTube

According to Rolling Stone, she took a redeye to New York and walked 13 blocks in the sleet, with hair that she'd purposely not washed for a week and a runny nose. That's how she got the role. 

5. Chris Hemsworth - the Thor/Avengers series 

It seems impossible to imagine anyone but Chris as Thor. But, as the story goes, Chris might have never been considered for the role, had it not been for some good, old-fashioned sibling rivalry. 

Chris and Liam Hemsworth
Source: ET

Originally, both Chris and Liam auditioned for the role, and while Chris never got a call-back, Liam was one of the four to five actors shortlisted for the role. However, Marvel was not too convinced with the final list, and the casting call was opened again. 

Chris as Thor
Source: ENCA

That's when Chris roped in his mother to help and channeled his frustration into making an audition tape that ultimately landed him the role: 

I did an audition in Vancouver in this hotel room with my mum reading Anthony Hopkins' part. She must have nailed it because it got me back in the room and that second audition was a lot different than my first one. I came in kind of with a little, I guess, motivation and maybe frustration that my little brother had gotten further than me. It's a little... sibling rivalry sort of kicked up in me.

                    - Chris to Looper

Chris Hemsworth as Thor
Source: Mens Health

It may not be the craziest story on the list, but it's certainly the one we are most glad about because, seriously, who else but Chris Hemsworth to play the God of Thunder?

6. Rupert Grint - the Harry Potter series 

When the casting call was made for the first Harry Potter film, Rupert, who went on to play Ron Weasley in the movies, heard about the audition on Newsround. While he had not done any professional acting before, he was a big fan of the books. 

Rupert Grint as Ron Weasley
Source: Insider

Consequently, he made a rap video on why he wanted to be Ron and the rest, as they say, is history. He even recited the rap once, at a press conference as an adult. And let's just say, we'd have cast him too! 

Rupert Grint
Source: Reddit

7. Amitabh Bachchan - Sholay

From lobbying for the role himself to asking Dharmendra to put in a good word for him, Amitabh Bachchan left no stone unturned in trying to land the role of Jai. Apparently, Salim Khan, one of the writers of the film, also recommended Amitabh Bachchan, going so far as to hold a screening of Zanjeer for the filmmakers, thereby alleviating any doubt about casting him in the role. 

Dharmendra Amitabh
Source: My Good Times

Additionally, according to Film Companion, Sanjeev Kumar, who went on to play the role of Thakur actually wanted to play Gabbar's role and Dharmendra, who was cast as Veeru, wanted to play Thakur's role. Sanjeev Kumar even offered to shave off his hair and blacken his teeth for Gabbar's role, but director Ramesh Sippy didn't agree. 

Sholay star cast
Source: News24online

8. Aditya Kumar - Gangs of Wasseypur

In an interview on the making of GoW, director Anurag Kashyap shared that actor Aditya Kumar used to approach him for work, constantly, after working with him on a short film. 'Irritated', Kashyap told him that if he could learn to play with a blade in his mouth, he'd cast him as Perpendicular in GoW, whenever the film was made. 

Kumar actually practiced with a blunt blade for 6 months, and then met Kashyap and showed him that he could, indeed, play with a blade. Visibly impressed, Anurag cast him as Perpendicular. 

Writing their own destiny!