Edmund Spenser’s poem Colin Clout’s Come Home Again, scholars agree, contains veiled references to fellow poets, including Samuel Daniel, Sir Walter Ralegh, and Sir Philip Sidney. Its dedication was signed in 1591, but Colin Clout was not published until 1595. Lines which are widely recognized as a memorial to Lord Ferdinando Stanley after his death in 1594 must have been added shortly before publication. The lines immediately following the tribute to Stanley may well have been added around the same time, and read:
And there though last not least is Aetion,
A gentler shepherd may no where be found:
Whose Muse full of high thoughts invention,
Doth like himself Heroically sound. 
The identity of "Aetion" is unclear--Michael Drayton, William Shakespeare, Thomas Sackville and William Stanley have all been suggested.  The interpretation I favor is that "Aetion" was an in-the-know reference to Christopher Marlowe. Marlowe certainly knew of Spenser. He somehow obtained a copy of Spenser's "The Faerie Queene" at least three years before it was published (Marlowe placed several lines from it in his Tamburlaine plays), and the two shared some of the same friends.
“Shepherd” was a term for poet, while “gentle” could mean mild, but also meant a person of distinction (the OED cites the example “gentle Jupiter”), one who was noble, one who was a gentleman, or one related to the “gentle craft,” a term for the occupation of Marlowe’s father, a shoemaker.
Elizabethans regularly capitalized names and nouns but not adverbs, and “Heroically” is the only adverb capitalized in Colin Clout’s Come Home Again. I suggest that “Aetion” represents a poet who is connected to someone named “Hero,” as Marlowe was through his authorship of Hero and Leander. A shepherd who “may no where be found” may refer to a still-living Marlowe who cannot be found, at least under his true name. According to this theory, the inference is that Aetion, i.e. Christopher Marlowe, was still alive when Spenser wrote about him in 1594 or 1595.