Salman Khan is probably the most generous star in Bollywood, and that is visible in the countless guest appearances, cameos and extended guest appearances he has done in films for his friends. In most of these films, he appeared in a song or a scene and wasn't required to act much. But there were a few occasions, which required him to act.
Below are the Top 5 Salman Khan Guest Appearances according to us:

Salman with Shahrukh in Kuch Kuch Hota Hai
Kuch Kuch Hota Hai
Salman played the charming Aman Mehra in this film and only appeared midway through the film. His role of a selfless love with a golden heart won over the hearts of the audience, and by the end of the film a section of the audience wanted Kajol's character to end up with Aman Mehra. That tells you of the oodles of charm Salman oozed in this movie. He also won the Filmfare Best Supporting Actor Award for Kuch Kuch Hota Hai.
Baghban
The current reigning Superstar of Bollywood played an orphan who was adopted and looked after by Amitabh Bachchan and Hema Malini. As Alok, he was required to play to the gallery and that is exactly what he did. Alok came to the rescue of Amitabh and Hema, when their own sons refused to take care of them. People loved him as the obedient son Alok, and that explains why he was signed up by Ravi Chopra again in Baabul.
Phir Milenge
According to Salman Khan himself, this was one of the most challenging roles of his career. He played an HIV positive guy called Rohit, who was the reason behind Shilpa Shetty contracting AIDS. He emoted the part as best as he possible could. His efforts were genuine and it showed. Even though the film failed commercially, it was a critically acclaimed film and Shilpa Shetty, Abhishek Bachchan and Salman got the accolades they deserved for such a brave film.
Saawariya
Salman's Imaan walked with the heroine (Sakina played by Sonam Kapoor) breaking the heart of Ranbir Kapoor. This was Salman's third film with Sanjay Leela Bhansali, and it was proved yet again that Sanjay Leela Bhansali brings out the best in Salman Khan. Imaan's past and present is shrouded in mystery and the mystery was brought out beautifully by Salman Khan.
Heroes
Salman played a Sardar for the first time in his career and had to mouth quite a few Punjabi dialogues. He had come out of his comfort zone to play Balkar Singh. Thankfully, he managed to do the job and played his character with an unique earnestness that is rarely seen in Salman's other cameos. His part of the story stayed with the audience long after the theatre lights were switched on
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