Very little biographical information is available on Rio, but according to infomations given in the letter column of the fotoromanzo magazine Sogno, he was born in Germany to Italian parents; his father being the Italian consul to Germany. The German Wikipedia more specifically states that he was born as Desiderio Letterio Ugo Nobile on 12 May 1897 in Berlin, citing the Landesarchiv Berlin as the source. However, the Wikipedia article also contradicts the info from the Sogno letter column by referring to him as a merchant's son.
Rio's film career began in German silent cinema in the early 1920s, and the IMDb lists him with appearing in a significant number of German films from the 1920s and 30s, but apparently only in very minor roles. Most of these films are very hard to come by, with many probably having been lost.
His switch to Italian cinema in the late 1930s looks to have come about due to the then-popular trend of shooting co-productions in different language versions, often with partially different casts. Rio appeared in a number of such German/Italian co-productions, and since he was fluent in both languages, he would appear in both the German and the Italian versions.
Having relocated permanently to Italy, Rio quickly became very active in Italian cinema. There is currently a bit of a gap in his filmography between 1942-49, which could at least partially be war-related, but otherwise he was very prolific, and thanks to his knowledge of German, he was very frequently cast as German-speaking characters, or other foreign types.
Rio continued to act right until the end. News of his death was reported by fotoromanzo actor/writer Carlo Mazzoni in his letter column in the magazine Sogno n. 18 (4 May 1961), stating that he had died in his native Germany, where he had gone to appear in a film.
- Der Dämon des Himalaya .... (credited, but not found)
1936 - Der Favorit der Kaiserin .... Nobleman (credited)
1937 - Il signor Max .... Cruise ship passenger (uncredited)
1938 - Inventiamo l'amore .... Party guest (uncredited)
- Solo per te .... The chauffeur (uncredited)
1939 - Due milioni per un sorriso .... Mr. Perotti's assistant (uncredited)
- Finisce sempre così .... Nightclub customer (uncredited)
- Follie del secolo .... Audience member in the theater (uncredited)
- Marionette .... Astori's associate (credited)
- Premiere der Butterfly .... (credited as "R. Nobile", but not found)
- Processo e morte di Socrate .... Man at the trial (uncredited)
- Retroscena .... Audience member at concert (uncredited)
1940 - Cuori nella tormenta .... Renato Giorgi (uncredited)
- Il ponte dei sospiri .... Member of the Council of Ten (uncredited)
- Piccolo alpino .... Austrian spy (uncredited)
1941 - Caravaggio, il pittore maledetto .... unknown role (no credit info)
- L'allegro fantasma .... Mr. Vernon, the impresario (uncredited)
- Marco Visconti .... Conspirator (uncredited)
1942 - 7 Jahre Glück .... Police chief (credited)
1949 - Yvonne la nuit .... The clown (credited as "Desiderio Nobile")
1950 - Domani è un altro giorno .... Party guest (uncredited)
- È arrivato il cavaliere .... Man in the Minister's entourage (uncredited)
- È più facile che un cammello... .... Foreign dignitary visiting the ministry (uncredited)
- Vita da cani .... Gossiping party guest (uncredited)
1951 - Bellezze a Capri .... Nightclub customer (uncredited)
- Cameriera bella presenza offresi... .... The Leonardi family's majordomo (uncredited)
- Il caimano del Piave .... Austrian officer (uncredited)
- Il microfono è vostro .... Policeman (uncredited)
1952 - Carica eroica ....German officer (uncredited)
- Tormento del passato .... Nightclub customer (uncredited)
- Totò e i re di Roma .... French officer (uncredited)
- Wanda, la peccatrice .... Man at the auction (uncredited)
1953 - I sette dell'orsa maggiore .... Giacomo (uncredited)
- La passeggiata .... Man at the ball in Paolo's dream (uncredited)
- La voce del silenzio .... A penitent (uncredited)
- Le infedeli .... Man at the cinema (uncredited)
- Roman Holiday .... Embassy officer at press conference (uncredited)
- Via Padova 46 ... Airplane passenger (uncredited)
1954 - Gli amori di Manon Lescaut .... Card player (uncredited)
- La Luciana .... One of the General Inspector's subordinates (uncredited)
- La schiava del peccato .... Factory manager (uncredited)
- Nel gorgo del peccato .... Nightclub customer (uncredited)
- Tempi nostri - segment "Scena all'aperto" .... Extra at the movie set (uncredited)
- Torna! .... Man at the casino (uncredited)
- Tradita .... Army doctor (uncredited)
- Una parigina a Roma .... Restaurant proprietor (credited)
1955 - Bravissimo .... The German family's butler (uncredited)
- Io piaccio .... Audience member in the theater (uncredited)
- Prigionieri del male .... German airplane passenger (uncredited)
1956 - Difendo il mio amore .... Party guest (uncredited)
- La fortuna di essere donna .... Party guest (uncredited)
- Le schiave di Cartagine .... Senator (uncredited)
- Londra chiama Polo Nord .... Military judge (uncredited)
- Mi permette babbo .... Man at the opera (uncredited)
- Totò lascia o raddoppia? .... Man who introduces Gagliardo to the countess (uncredited)
- Totò, Peppino e i fuorilegge .... Tabarin customer (uncredited)
- Una pelliccia di visone .... Businessman (uncredited)
1957 - C'è un sentiero nel cielo .... Party guest (uncredited)
- Femmine tre volte .... Roulette player (uncredited)
- La canzone del destino .... Café customer (uncredited)
- Serenate per 16 bionde .... Audience member at the music show (uncredited)
- Totò, Vittorio e la dottoressa .... Nightclub customer (uncredited)
1958 - Adorabili e bugiarde .... Judge (uncredited)
- Amore e chiacchiere .... Guest at Paseroni's house (uncredited)
- La zia d'America va a sciare .... Man in hotel nightclub (uncredited)
- Ladro lui, ladra lei .... Vatican librarian (uncredited)
- Le bellissime gambe di Sabrina .... Bar customer (uncredited)
- Nata di marzo .... Man at the conference (uncredited)
- Totò nella luna .... Officer at the top secret Pentagon meeting (uncredited)
1959 - Annibale .... Senator (uncredited)
- Fantasmi e ladri .... Man who congratulates Annunziata on catching the thieves (uncredited)
- Il generale della Rovere .... SS officer (uncredited)
- Il raccomandato di ferro .... General (uncredited)
- La cambiale .... Nightclub customer (uncredited)
1960 - La dolce vita …. Nightclub customer (uncredited)
- "Principessa in esilio" (Published in Sogno from July to December 1951)
- "Difendo il mio amore" (Published in Sogno from January to June 1952)
- "L'adorabile intrusa" (Published in Sogno from April to August 1952)
- "Felicità proibita" (Published in Sogno from June to October 1952) - credited
- "Raggio di sole" (Published in Sogno from June to November 1953) - credited
- "Il mio amore sei tu" (Published in Cine Illustrato from June to November 1953)
- "Ho scelto il tuo amore" (Published in Sogno from November 1953 to April 1954)
- "Pagherai per le mie lacrime" (Published in Cine Illustrato from November 1953 to May 1954)
- "Addio Pisana" (Published in Sogno from April to October 1954) - credited
- "Fior di Siviglia" (Published in Tipo from August 1954 to early 1955)
- "Labbra serrate" (Published in Cine Illustrato from December 1954 to May 1955)
- "I tuoi occhi hanno paura" (Published in Cine Illustrato from March to September 1955) - credited
- "Amore vince rancore" (Published in Sogno from March to August 1955) - credited
- "Un abisso tra noi" (Published in Luna Park from May to August 1955)
- "Il prezzo dell'onore" (Published in Cine Illustrato from July to November 1955)
- "Amore di principessa" (Published in Luna Park from November 1955 to March 1956) - credited
- "Da qui alla felicità" (Published in Cine Illustrato from March to August 1956) - credited
- "La voce del sangue" (Published in Cine Illustrato from March to August 1956) - credited
- "In nome del cuore" (Published in Cine Illustrato from August to December 1956)
- "Una donna si ribella" (Published in Sogno from October 1956 to March 1957) - credited
- "Una donna fortunata" (Published in Cine Illustrato from December 1956 to May 1957)
- "La morte del cigno" (Published in Sogno from December 1956 to May 1957)
- "Paura di te" (Published in Cine Illustrato from February to June 1957) - credited
- "Mamma, perdonami" (Published in Luna Park from February to June 1957) - credited
- "Più forte del male" (Published in Sogno from May to October 1957)
- "La sepolta viva" (Published in Sogno from September 1957 to January 1958) - credited
- "Regina del mio cuore" (Published in Polvere di Stelle from September 1957 to March 1958) - credited
- "L'orgoglio ti perderà" (Published in Cine Illustrato from November 1957 to May 1958)
- "Cuori feriti" (Published in Sogno from January to May 1958)
- "La tragedia di Mayerling" (Published in Sogno from June to December 1958) - credited
- "Le due orfanelle" (Published in Cine Illustrato from November 1958 to April 1959) - credited
- "È caduta una stella" (Published in Polvere di Stelle from January to July 1959) - credited
- "Selvaggio come l'amore" (Published in Sogno from October 1959 to February 1960)
- Die Dame in Grau (1922) IMDb
- Das Wirtshaus im Spessart (1923) IMDb
- Zwischen Flammen und Bestien (1923) IMDb
- Rosenmontag (1924) IMDb
- Bismarck, 1. Teil (1925) IMDb
- Amor auf Ski (1928) IMDb as Count von Golz
- Der Fremdenlegionär (1928) IMDb as French officer
- Durchlaucht amüsiert sich (1932) IMDb as The cousin
- Abenteuer eines jungen Herrn in Polen (1934) IMDb
- Herr Mahler in tausend Nöten (1934, short film) IMDb as A gentleman
- Barcarole (1935) German Wikipedia as A celebrating Venetian
- Ein idealer Gatte (1935) IMDb as Servant of the Chiltern Family. I was unable to find Rio in the version posted on YouTube, but the quality was so atrocious that I could easily have missed him. He is not credited.
- Eine Seefahrt, die ist lustig (1935) IMDb as SR
- Das Schloß in Flandern (1936) IMDb as Clifton
- Der Abenteurer von Paris (1936) IMDb
- Fridericus (1937) IMDb as French courtier
- Gleisdreieck (1937) IMDb as 2nd criminal investigator
- Mutterlied (1937) IMDb as The chauffeur. This is the German-llanguage version of Solo per te, in which Rio is confirmed to appear in the same role.
- Weiße Sklaven (1937) IMDb as Young officer. I have searched for Rio in this one without success, but the only available print was quite poor so I could have missed him. He is not credited in the rather lenghty cast list.
- Mia moglie si diverte (1938) ANICA
- Partire (1938) ANICA as Mattia, the chauffeur
- Unsere kleine Frau (1938) IMDb. This is the German-language version of Mia moglie si diverte.
- Casa lontana (1939) ANICA as Chauffeur
- Castelli in aria (1939) ANICA
- Der singende Tor (1939) IMDb. This is the German-language version of Casa lontana.
- Dir gehört mein Herz (1939) This is the German-language version of Marionette, in which Rio is confirmed to appear as Astori's associate, so he presumably plays the same role here.
- Il sogno di Butterfly (1939) ANICA. This is the Italian-language version of Premiere der Butterfly, in which Rio is credited but was not found.
- Divieto di sosta (1941) ANICA
- 7 anni di felicità (1942) ANICA as Police agent. This is the German-language version of 7 Jahre Glück, in which Rio is confirmed to appear.
- La guardia del corpo (1942) ANICA
- Angelo tra la folla (1950) ANICA. According to IMDb he plays the role of Blumfield.
- Romanticismo (1951) ANICA
- Quattro rose rosse (1952) ANICA
- La regina di Saba (1952) ANICA
- Nessuno ha tradito (1953) ANICA
- Mamma sconosciuta (1956) ANICA as Hotel manager
- Altri tempi (1952) ANICA and IMDb list with playing an Austrian officer in the segment "Il tamburino sardo". This sounds like a typical role for him and there are a few Austrian officers, but they are filmed only from a great distance, so if Rio does appear then he is not recognizable on-screen. He is not credited.
- Suchkind 312 (1955) German Wikipedia claims this was the first German film Rio appeared in after WW2, but he's nowhere to be found in this film and is not credited either.