Near the end of time, the last member of the timeline-managing Time Variance Authority oversees the birth of three entities named Ast, Vort, and Zanth; these three become either the Time-Keepers or the Time-Twisters in one of the two possible remaining futures. The Time-Keepers are the employers of Immortus, and use him to eliminate timelines In finance, volatility (symbol σ) is the degree of variation of a trading price series over time, usually measured by the standard deviation of logarithmic returns.. Historic volatility measures a time series of past market prices. Implied volatility looks forward in time, being derived from the market price of a market-traded derivative (in particular, an option).