Upon reaction of gaseous Me3SiF with the in situ prepared Lewis acid Al(ORF)3, the stable ion‐like silylium compound Me3Si‐F‐Al(ORF)31 forms. The Janus‐headed 1 is a readily available smart Lewis acid that differentiates between hard and soft nucleophiles, but also polymerizes isobutene effectively. Thus, in reactions of 1 with soft nucleophiles (Nu), such as phosphanes, the silylium side interacts in an orbital‐controlled manner, with formation of [Me3SiNu]+ and the weakly coordinating [FAl(ORF)3]– or [(FRO)3Al‐F‐Al(ORF)3]– anions. If exchanged for hard nucleophiles, such as primary alcohols, the aluminum side reacts in a charge‐controlled manner, with release of FSiMe3 gas and formation of the adduct R(H)OAl(ORF)3. Compound 1 very effectively initiates polymerization of 8 to 21 mL of liquid C4H8 in 50 mL of CH2Cl2 already at temperatures between −57 and −30 °C with initiator loads as low as 10 mg in a few seconds with 100 % yield but broad polydispersities.