Methionine is a non-polar amino acid and is one of the only two amino acids to contain a sulphur group. However, unlike cysteine, it cannot form sulphur bridges (a covalent bond between two sulphur atoms, used to stabilise the 3D structure of some proteins) as there is no hydrogen attached to the sulphur. Methionine is an intermediate in the synthesis of compounds such as lecithin and taurine, along with many others, mostly phospholipids.
A derivative of methionine, N-formylmethionine, is always used as the initial amino acid in translation in bacteria and methionine is always found in the beginning of eukaryotic proteins although is often removed during post-translational modification. The reason for both of these is that methionine is coded for by the codon AUG, the same as the start codon for translation.
Methionine is an essential amino acid in humans although other organisms (including other mammals) can synthesise methionine from aspartic acid and cysteine. This is a multi-step process requiring both ATP and NADPH.