The conducting of Carlos Kleiber (1930–2004) was, and is, revered. The film of his astounding Brahms 2 (1991) is tucked away in my post Conducting from memory, where I have hardly managed to expand the global audience it so deserves. The YouTube link comes and goes, but you can find it
Be spellbound by the coda of the 1st movement (from 12.52), with the horn solo introducing the violins playing high on the G string… and then the slow movement!!!
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In Norman Lebrecht’s The maestro myth, Carlos Kleiber and his father Erich appear in the chapter “The mavericks”, along with Horenstein, Celibidache, and Tennstedt. See also e.g. Declan Kennedy on “the Kleiber myth”, referring to Carolyn Watson’s thesis, and Tom Service’s tribute.
Reclusive and mercurial, Kleiber shunned the press, and was averse to recording. Even in the rather few concerts that he took on, he often seemed to be more presiding than conducting—trusting in the musicians.
Kleiber’s use of free bowing for his 1991 Brahms 2 was unusual; generally he carefully prepared the orchestral parts in advance. From film I am lost to the world (see below), from 34.42.
However, whereas Rozhdestvensky was minimalist both in both gesture and rehearsal, I was bemused to learn that Kleiber’s apparent spontaneity on the platform was the result of fastidious preparation (see viola part above) and an inordinate amount of rehearsal. Even with continental orchestras already used to far more rehearsals than their British counterparts, he demanded up to five times more than other maestros—and for a repertoire that the musicians already knew well, to boot;  you’d think the band would be able to perform from memory too (cf. my note on Celibidache). Anyway, this rather explains Kleiber’s economy of gesture on stage; his micro-management in rehearsal gave him freedom in performance. As he declared,
With a good technique, you can forget technique.
Indeed, Kleiber claimed to dislike conducting. “I only conduct when I am hungry”; “I want to grow in a garden, sit in the sun, eat, drink, sleep, make love, and that’s it.” Still, he could play the prima donna.
We’re fortunate to have several films of his performances; all the petty detail of rehearsal is forgiven when we see him in concert.
Tristan at Bayreuth, c1974–76:
While Kleiber’s main projects were in the opera house (La Traviata, Rosenkavalier, Wozzeck, and so on), his orchestral concerts were also sensational.
Temporarily absent from YouTube is his 1991 performance of Mozart’s Linz symphony with the Vienna Phil (this is definitely no time for me to go all Early Music on you; and for the orchestra’s resistance to gender equality, see note here).
Beethoven 7  with the Concertgebouw (1983):
Just as gorgeous as Kleiber’s Brahms 2 is his Brahms 4, which he recorded several times. Here’s a live performance with the Bayerische Staatsorchester in 1996—a rare occasion when he had a score in front of him, but don’t worry, it’s merely ornamental. Currently it appears on YouTube in instalments—here’s the opening:
(3.33 milking mice again!)—a crafty link: Die Fledermaus overture (a piece not to be sniffed at) from 1970, in rehearsal and (from 36.15) performance:
And here, split-screen shows how Kleiber conducted performances of the overture in 1986 and 1989—his different gestures deriving largely from the greater familiarity of the Vienna orchestra (on the right) with the piece:
From Johann to Richard Strauss—an audio recording of a live 1993 performance of Ein Heldenleben with the Vienna Phil: 
See also The art of conducting: a roundup.
 I guess someone must have researched the history of rehearsal in WAM; certainly Bach’s musicians were used to performing unfamiliar music every week with a minimum of preparation, but it’d be interesting to learn the timeline for expanding rehearsal times, and budgets, over the 20th century (and how British orchestras rarely afforded them).
 Wagner’s description of the symphony as “the apotheosis of the dance” is irritatingly famous, his authority presumably resting on years as a regular on the Bayreuth clubbing scene; for a different kind of transcendence, try Moroccan ahouach, or Northern soul (cf. What is serious music?!).
 Strauss completed Ein Heldenleben in 1898—between Mahler’s 3rd and 4th symphonies. Dedicated to Willem Mengelberg (whose own 1928 recording is here; we can even hear Strauss himself conducting it in 1944), it continues to divide opinion. Perhaps Strauss rather shot himself in the foot by providing such an explicit programme: had he merely presented the work as an abstract symphonic poem with the usual contrasts of yin and yang (actually not value-free, as Susan McClary stresses!), it might have been free of the taint of master-race ideology—if not of this kind of criticism (another of the scurrilous reviews assembled by Nicolas Slonimsky):
The composer indulges in self-glorification of the most barefaced kind… The Hero’s antagonists are described by him with the utmost scorn as a lot of pygmies and snarling, yelping, bowwowing nincompoops… The climax of everything that is ugly, cacophonous, blatant, and erratic, the most perverse music I ever heard in all my life, is reached in the chapter “The Hero’s Battlefield”. The man who wrote this outrageously hideous music, no longer deserving of the word music, is either a lunatic, or he is rapidly approaching idiocy. (Otto Floersheim, Musical Courier 1899).
Later pundits—if not musicians and audiences—have generally concurred: Norman Lebrecht considers Heldenleben “tacky in every way, a blob of sensationalist Nietschean philosophy bound together with orchestral virtuosity and no nutritional substance”. No pleasing some people… Don’t let all this quibbling deafen you to the transcendent final movement! See also under Melody: the major 7th leap.
For more on Richard Strauss, see Metamorphosen.