Björn von Knorring
The picture is a swedish cartoon-figure Herman Hedning. English info here: https://en.m.wikipedia.org/wiki/Herman_Hedning
Can Guards of the citadel be played by the FP player if Minas Tirith is occupied by Shadow units under siege?
Yes. You can always muster with event cards even when under siege but you cannot muster with action dices when under siege.