*An actors job is to act and that to any character without any choice that whether it is a negative-villainous character or a comedy one or it is close to real life one.
There are many actors, from the time of inception of Malayalam cinema, who could be classified as versatile actors. Early days of Malayalam cinema saw few stalwarts like Satyan, Thikurussi Sukumaran Nair, Kottarakara Sreedharan Nair, Prem Nazir, Adoor Bhasi, Madhu and so on. Prem Nazir was a pure commercial hero like M.G.R. in Tamil & Raj Kumar in Kannada or NTR/Nageshwar Rao in Telugu. THikkurussi had an acting style that suited that era. Madhu was good actor but faded in the Charisma of Prem Nazir and energy of Satyan. Adoor Bhasi was always the best comedian for Malayalam cinema along with Jagathy sree kumar. Satyan was widely believed to be a great actor of that era but my favourite was Kottarakara Sreedharan Nair. His performance in Chemeen and aranazhika neram speak for itself.
In the 80s there came up an actor who won a national award for best actor in his first film as hero. That was none other than Bharath Gopi or Kodiyettam Gopi.Bharath after the Bharath Award & Kodiyettam after the film kodiyettam, the film which he had won the award. Gopi instilled life into Malayalm cinema. His acting made people feel that he was living and not acting. He acted his way to glory untill he was paralysed. He could enact any role.from an imbecilic in kodiyettam to a grand father in revathikkoru pavakutty.from a turmoiled father in mamattykutty amma to job seeker in akkare. His negative roles made an impact. Even in peak of his career he acted in small meaty roles and negative roles.
Mohan lal is the soul of Malayalam cinema. Mohanlal and Mammooty brought a culture that was unknown to Malayalam cinema before, although Prem Nazir enjoyed that a bit in his peak.the super star culture. But, surely Mohanlal stands top in acting, because of his inborn talent, versatility, dedication, hard work and so on. Mohanlal never resorted to gimmicks like acting 10 roles in a film like actors who claimed themselves as great actors. Mohanlal acted in simple films, lived the character and made the people recognize that he is a genius in acting. His films had been discussed in many a platform and hence I am not going into that.
Nedumudi venu is an actor who was never glorified. He is totally an unsung hero. His versatality is tremendous similar to Bharat Gopi and Mohanlal. His acting prowess in films like Thakara, vidaparayum munbe, minnaminunginte nurunguvattom(he lost the national award to kamalhasan un the last round for his acting in this film)are worth mentioning. He had slip to stereo type old man roles later, there by movie goers lost an actors versatile genius.
Thilakan is just a character artists technically, but he is again one of the actors in Malayalam cinema who can act any kind of role except a chocolate hero. His acting gave the movie goers a new world of realism, relating them to the real life. Thilakan is one of my pick. There are many films to be mentioned.
Finally Jagathy Sree Kumar, the comedian who is ruling thr roost in Malayalam cinema for the past many decades. When Adoor Bhasi left, no one believed that Malayalam cinema will have a comedian like him again. Jagathy could act in any way. He even overacted whenever required. He could act any kind of character. At times he was a Jim Carrey but he could enact Anthony Hopkins.
This is my list
Bharat Gopi
Mohan Lal
Nedumudi venu
Thilakan
Jagathy Sree Kumar
Other actors worth mentioning here are Kottarakara, Murali, Sai Kumar, Sreenivasan, Siddique, Mammooty and Satyan.