For bishops of Syriac tradition (Oriental Orthodox and Catholic) the title "Mar" is not used in the article name unless necessary for disambiguation or for conformance with actual usage. Thus Varkey Vithayathil is used, not "Mar Varkey Vithayathil" or forms such as "Mar Varkey Cardinal Vithayathil". However Mar Thoma I, Mar Thoma II, etc. are used, because these men are never referred to as simply "Thoma I" etc.
Read more about this topic: Wikipedia:Naming Conventions (clergy)