John Sincler (Sinklo, Sincklo) is known in theater records primarily by the appearance of his name in publications of plays and the manuscript of a plot. For example, his name ("Sincklo") appears in the quarto of 2 Henry VI, which was printed in 1600 when the play is known to have been in the repertory of the Chamberlain's men (Nungezer, p. 326). But Pembroke's men are known to have had a version of that play in repertory in 1592-3 (under the title of The First Part of the Contention betwixt the two famous Houses of Yorke and Lancaster). A similar confusion occurs with Sincler's name in a stage direction in The Taming of the Shrew, the early stage history of which is entangled with that of The Taming of a Shrew (initially printed with an advertisement of Pembroke's men on its title page). Likewise, the appearance of his name in the earliest printed edition of 3 Henry VI fails to date Sincler's joining the Chamberlain's men not only because there is no pre-folio edition of the play but also because scholars do not agree on the stability of the text from its initial version to its first publication in 1623. A better marker may be his name in the quarto of 2 Henry IV (1600), "where Mrs. Quickly calls the beadle whom he played an'Atomy' ..., which suggests that he was either unusually small or unusually thin" (Eccles, p. 168).
Another kind of confusion occurs with the presence of Sincler's name in the plot of "The Seven Deadly Sins, part two," which past generations of theater historians assigned to Lord Strange's men in the early 1590s but which in 2004 was persuasively reassigned by David Kathman to the Chamberlain's men c. 1597.
There is however no question that Sincler was a member of the Chamberlain's men in the 1590s and the King's men beyond. He was named among the players in the newly-written Induction to The Malcontent, which the King's men performed in 1604. His roles suggest that he was a hired man.
Keeper, Warden in "Induction"; Soldier in "Envy"; Captain, Musician in "Sloth" in Part two of "The Seven Deadly Sins"
Eccles names several women who may have been Sincler's wife: Elizabeth "Synckler," who sought sureties of the peace in 1593 (p. 168); and Elizabeth "Sinckley," designated "widow," who was a recusant in 1611 (p. 168). Yet another is Bettrice Sinckloe, who was "buried on 27 January 1620/21 at St Leonard, Shoreditch, from Holywell Street" (p. 169).