John Sincler 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). 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 beyond. He was named among the players in The Malcontent, which the King's men performed in 1604. Scholars deduce from comments made about Sincler in his own time that he was small and slim. His roles suggest that he was a hired man with the Chamberlain's men.
Part two of "The Seven Deadly Sins":
Keeper, Warden in "Induction"; Soldier in "Envy"; Captain, Musician in "Sloth"