Howells, who lived in Glasgow, is understood to have died on Monday.
Known for his one-to-one performances that involved intimate actions such as washing the audience member's feet, bathing, or doing laundry, Howells was a creative fellow at Glasgow University's Department of Theatre, Film and Television, as well as an artist in residence at the Arches venue in Glasgow.
Howells had a reputation for innovative theatre work both nationally and internationally and was also well known for working with emerging artists and students.
Jackie Wylie, artistic director at The Arches, said: "It is devastating for everyone who was touched by Adrian.
"So many would say that there truly was no one like him, who personified love, generosity and the deepest type of empathy and desire to understand those lucky enough to have met him.
"With great humour he was able to create an instant connection with anyone he encountered.
She added: "He supported, encouraged and was at the heart of an entire community of artists in Glasgow who will miss him terribly."
Neil Murray, executive producer of the National Theatre of Scotland, said Mr Howells had been a great influence on a generation of theatrical talent.
Mr Murray said his sudden death had come as a great shock to friends and colleagues.
"It's just devastating, it will affect people in Glasgow and in Scotland, and it will be felt around the world," he said.
"He had an extraordinary way of connecting with people."