CASSIUS: You gods, it doth amaze me
A man of such a feeble temper should
So get the start of the majestic world
And bear the palm alone.

William Shakespeare (1564–1616) English dramatist and poet

Julius Caesar, Act 1, sc. 2, l. 135ff (1.2.135–138) (1599)
    (Source)

"Temper" is used here in the sense of the temper of metal, reflecting on Caesar's just-described bodily weakness.