Zel·ig also zel·ig 
(zĕlĭg)
(zĕlĭg)n.
1. One who unconsciously mimics the traits or appearances of those with whom he or she associates.
2. One having a ubiquitous, often inconspicuous presence: "[He] is a sort of Zelig of modern politics, popping up and blending in at momentous occasions" (Alessandra Stanley).
[After Leonard Zelig, the main character of the film Zelig (1983) written and directed by Woody Allen .]