Järegård had a taste for villainous and dark characters, and enjoyed playing them. But he also had a very lyrical and soft side to him as an actor, something he showed in the TV production of Hans Christian och sällskapet (where he plays a village priest who suffers a great personal tragedy as his wife loses her mind after having a baby) and in the TV adaptation of Birger Sjöberg's Frida och hennes vän (based on Sjöberg's Frida's Book) where he plays the light-hearted, daydreaming early 1900s love-struck suitor of Frida. Adding the fact that Järegård also had a beautiful and expressive singing voice (he performed in a number of stage musicals during his career) gave him an incredible range and versatility as an actor. He originated the role of Guido in the first European staging of the musical Nine, for example (Oscarsteatern, Stockholm, 1983).
Järegård went on to play the villainous character Elaka Måns (Mean Mike in the English dub) in the Swedish animated movie Peter-No-Tail and its sequel Peter-No-Tail in Americat. He also lent him voice for the Swedish dub of the film Valhalla, playing the Norse God Loki; god of mischief.
Järegård gained international attention when he took on the role of Doctor Helmer in Lars von Trier's highly acclaimed mini-series Riget and Riget II (aka The Kingdom I & II). He also appeared in von Trier's Europa. He participated in about 20 movies and 40 TV productions: aside from the Riget-series; some of his greatest roles are in the Skånska mord-series, in the 1975 Hasse & Tage comedy Släpp fångarne loss, det är vår! (Release the Prisoners to Spring), in the 1962 cult movie Raggargänget, in Kådisbellan (aka The Slingshot) in 1993 and as the pompous old drag queen Ragnar Rönn in the teleplay Cheek to Cheek (written and directed by Jonas Gardell), 1997. Also in 1997 he appeared in CHOCK as the series' host and presented each episode. Usually he would make elaborate philosophical and mystical statements regarding the plot of each episode.
For his acting work, he was awarded with the Thalia prize (1967) and the Eugene O'Neill Award (1975), two of Sweden's most prestigious theatre awards.
Järegård was a very colourful theatre personality who loved to stand out and celebrated originality. He loved clothes and Italian designers and was picky with designer labels in private – only the best would do. He was of the old belief that as an actor you not only represent yourself as a public person but also the theatre and the art as a whole; as being part of a public institution there for people; and therefore it is an actor's responsibility to "scrub up".[citation needed]
In his director's commentary on the DVD release of Europa, Lars von Trier commented that Järegård was difficult to work with, frequently sulking and making outrageous demands such as insisting on staying in one specific room in a specific hotel of his choice. He stated that Järegård was a compulsive scene-stealer who could not help attracting the focus even when he was supposed to be in the background of a scene. Von Trier claims that he eventually 'trained' Järegård by rewarding him with cigars for good behaviour but also called the actor "dear Ernst-Hugo" and said he misses him terribly. [citation needed]