Tiger and Elin (in happier days) were certainly on the same page when it came to choosing unisex names for their kids. Their first child, daughter Sam Alexis, sports two names that can be assigned to either gender, as does Charlie Axel.
They are also part of a larger trend of naming children with nicknames. They could have easily gone with Charles, but instead opted for Charlie. This is much like how Jamie Lynn Spears went with Maddie instead of Madeleine. Or, how Kate Winslet named her son Joe instead of Joseph.
Charles has always been popular. It’s German for “free man,” and rose to popularity in France in the middle ages due to Charles the Great. Some more recent references? Charlie’s Angels, Charlie Chaplin, and jazz legend Charlie Parker.
Axel — though it may sound a little figure skate-ish in the US – is actually very popular in Scandinavian. The name, which is a biblical word for “father of peace” was chosen by Elin’s mother to honor her older brother, who bears that name.