Louis Gentile

He began his studies in New York as a baritone, but switched to tenor before completing his training. After winning a few singing competitions, he became a member of the studio of the Zürich opera theater. 1983–86, he sang in Darmstadt, 1986–88 at the United Theaters of Krefeld and Mönchengladbach, where he had his first major successes as Alfredo and as Gösta Berling in Zandonai's Cavalieri di Ekebù. Guest appearances in Vienna (Kammeroper), Oslo, Berlin (Staatsoper) and Amsterdam.

In 1990, he stepped in as Hoffmann at the Deutsche Oper Berlin, with no previous rehearsal, and won a big success. He sang in Wiesbaden, at the Munich Gärtnerplatztheater, in Bielefeld, Gent, Bonn, Sevilla, Antwerpen, again in Amsterdam and Oslo, in Rome, Sevilla, and one single performance at the Vienna Staatsoper.

His repertory was particularly wide: Almaviva, Tamino, the title role in L'Ormindo by Cavalli, Don José, Erik, Rodolfo, Jeník, Max, Tannhäuser, Tristan, Pedro, Tambourmajor, and lots of contemporary opera, including some world premieres.
Reference: Kutsch & Riemens

François Nouvion didn't quite like Gentile, as is obvious from what he wrote about him:

Gentile had several vocal deficiencies that did not get better with time. He was soon in demand to replace sick heldentenors. He was singing Tannhäuser in Munich, replacing a sick colleague, and wobbled all the evening. We can hear the same type of singing in another Tannhäuser in an horrible Geneva production that did not help him either. (The production must be seen to be believed.) At the beginning of his career, he was given, thanks to a friend, a role as one of the armed men in the Magic flute. He did not show up without informing anybody, invoking later that the role was too small for him. He is a great cartoonist and liked to make fun of people by posting on opera house bulletin boards, where he was singing, cartoons of people in charge. A fact that did endear him with management and finally got him fired.

So Gentile seems to have been kind of an operatic rebel, which is not the worst of all things in my opinion. About his Tannhäuser, it's all true that it's no fun to listen to, not even in other (supposedly more successful) productions; but on the other Wagnerian hand, he left some traces on Youtube as a very good Tristan. Personally, I've heard him only in the early stage of his career, and he could be excellent at that time (I fondly recall a Pagliacci production directed by George Tabori at the tiny Vienna Kammeroper with Gentile as Canio, where he excelled also as an actor).
Both before and after his operatic career, Gentile sang (and played the guitar) in a rock and pop band (he had his own pop band as early as age 15, and toured the USA quite successfully with that band). On his website, you can hear him both in opera and in rock songs like "Pretty woman" or "Lucy in the sky with diamonds", and you can proceed to a Facebook page dedicated to his (actually extraordinary) cartoons.