Caption: Actors before Hamlet (Act II, Scene 2 (scroll down ∼ 80 %) of Hamlet (c. 1601)), Wladyslaw Czachorski (1850--1911), 1875.

Left to right: Rosencrantz and Guildenstern, Hamlet, Polonius, Player King, Player Queen, Spear Carrier, Rigoletto, Albrecht Duerer (1471--1528).

From a bit earlier in Hamlet:

Welcome, dear Rosencrantz and Guildenstern!
Moreover that we much did long to see you,
The need we have to use you did provoke
Our hasty sending. Something have you heard
Of Hamlet's transformation; ...

---Claudius, Act II, Scene 2 (at top) of Hamlet (c. 1601), William Shakespeare (1564--1616).

I'll just assume it's all true.

Rosenkrantz would later meet Johannes Kepler (1571--1630). The link between Kepler and Shakespeare is thus established---I knew there had to be one. They may never heard of each other---although Kepler's fame as Imperial Mathematician (i.e., essentially court astrologer) to the Holy Roman Emperor Rudolf II (1552--1612, reigned 1576--1612) may have penetrated to England---but there was only 1 degree of separation (see Wikipedia: Six degrees of Separation).

Kepler in 1600 during his first period with Tycho Brahe met with Rosenkrantz, Tycho's third cousin (Thoren 1991, p. 427--429; Casper 1993, p. 107--108). Since Kepler traveled briefly with Rosenkrantz, they must have communed at least a little. Like Tycho, Rosenkrantz was of the Danish nobility and was highly educated. Tycho reports that he knew Latin, Italian, French, Spanish, and German---and he spoke Danish---but no mention of English.

In 1600, Rosenkrantz was down on his luck---he'd had an affair with Danish lady-in-waiting Rigborg Brockenhuus (1579--1641) who got pregnant. Weighed against the centuries, this seems small enough---but as Hamlet remarks

... conception is a blessing;
but not as your daughter may conceive.
Friend, look to't.
--- Act II, Scene 2 (scroll down ∼ 30 %) of Hamlet (c. 1601), William Shakespeare (1564--1616).

Rigborg was sentenced to life imprisonment---but was eventually let out and allowed to live with her son Holger. Rosenkrantz was banished and ordered join the war against the Ottmoman Empire (must be Long Turkish War (1593--1606))---in other words, ordered to go on a crusade. It was on the "road to Jerusalem" that he visited Tycho in 1600 April. Rosenkrantz died in 1602 in duel---he was trying to stop it, NOT fight it.

I believe it is absolutely certain that in 1592 in his earlier adventure to England, Rosenkrantz and his sidekick Gyldenstierne (see Alien images file: alien_rosencrantz.html and the figure above (local link / general link: alien_rosencrantz.html)) were noticed by Shakespeare as archetypical Danish noblemen. Maybe Shakespeare saw them in a parade or maybe they were merely spoken of in the Mermaid Tavern. But somehow they caught his attention and Shakespeare cast them---I know it's them---in bit parts in Hamlet. In the 20th century, Tom Stoppard (1937--) gave them---I know it's them---title roles (also starring roles) in Rosenkrantz and Guildernstern are Dead (1966). It is fitting that Rosenkrantz has become an immortal.