Michael Ironside will be appearing in The Flash Season 2 as Lewis Snart, the "estranged, abusive...career criminal" father to Wentworth Miller's Captain Cold/Leonard Snart and Peyton List's Golden Glider/Lisa Snart.
The apple doesn't fall far from the tree, as Lewis is described as a cold-blooded, ruthless career criminal. Recently released from prison, he returns to Central City with a plan that will endanger both of his children. In the comics, not much is known about the Snart patriarch other than the fact that he was so abusive to his son — the future Captain Cold — that the boy spent more time with his grandfather who ran an ice truck.
At The Flash SDCC panel, executive producer Andrew Kreisberg did mention that we'd be seeing more of the Snart family on The Flash, though it wasn't clear he meant we'd actually be meeting new members. And of course this casting opens up an opportunity for Ironside to guest-star on Captain Cold's other show, Legends of Tomorrow.
Smallville fans will remember that Ironside has already played List's father on The CW's DC TVverse, as General Sam Lane to List's Lucy Lane. Both were great in the roles, and it will be fun seeing them reprise their (evidently less cozy) familial bond in Central City.