Iyengers ....

Iyengar or Ayyangar is a caste given to Hindu Brahmins of Tamil origin who follow the Visishtadvaita philosophy propounded by Sri Ramanujacharya. They are found mostly in Tamil Nadu as they are generally native to the Tamil country. But they are also found in large numbers in Karnataka and Andhra Pradesh.

Iyengars are Pancha Dravida Brahmins. Their actual mother tongue is Tamil. But nowadays there are Iyengars who speak other languages, mainly Telugu, Kannada, Hindi and Malayalam.
Vaishnavites have been living in the Tamil country even prior to the time of Ramanuja. However, Iyengars as a community trace their origin from the times of Ramanuja. However, in many cases, both Iyers and Iyengars are mistakenly referred to as "Ayyar" as they are indistinguishable from Iyers in their adherence of the Brahmanaical tradition. However, devout Iyengars sport a namam (thiruman+srichoornam) as a caste-mark as opposed to Iyers who apply vibhuti.

The word "Iyengar" is a relatively new name and was not used in any medieval works or scriptures. The word "Sri Vaishnava" would therefore be the right word to describe them, though all of them could be called as Sri Vaishnava Brahmins. The word Iyengar is derived from Ayya a Prakrit version of the Sanskrit word Arya along with the Telugu honorific plural suffix garu. Some others believe that the word "Iyengar" means one who is characterized by five attributes (Aindu angangal).
Though Vaishnavite deities have been worshipped in the Tamil country at least since the beginning of the 1 A.D, the origin of Iyengars as a separate community dates from the 10th century AD when Ramanuja lived.
Iyengars are divided into two different sects, namely Vadakalai and Thenkalai.
The Iyengar community started taking shape about 1000 years ago, and traces its philosophical origins to Nathamuni, a Sri Vaishnava Acharya, who lived around 900 CE. Ramanuja claimed that the mystic insights of the Azhwars were the same truths enshrined in the Vedas, and created a group of people whose identity as servants of Narayana focussed on the fact that all sentient beings were 'equal' being children of the same Supreme Being, and that outward bodily differences in terms of varna and caste were unimportant in terms of one's relationship to the Supreme.
By philosophy Iyengars are classified into Vadakalai, or "Iyengars of the Northern Descension", and Thenkalai, or "Iyengars of the Southern Descension", with subtly different philosophical and ritual interpretations of Ubhaya Vedanta. Scholarly opinion is mixed as to the origin of the two names. Some believe that the terms Northern and Southern refer to differing regional developments, the Northern or Vadakalai predominating in the north of the Tamil country and the Southern or Thenkalai predominating in the south. Others argue that they reflect the importance or primacy given to Sankrit Vedanta by the Vadakalais and of the Tamil scritpure, Divya Prabandham, by the Thenkalais.
Some others argue further that the difference is also racial, with the opinion that the Vadakalai sect descend from Indo-Aryan missionaries whereas the Thenkalai sect descend from various groups, some ancient Brahmin groups that are not as 'Aryan' as the Vadakalais, suggesting Dravidian admixture, and that some also descended from converts to Sri Vaishnavism from non-Brahmin ethnic groups.
The Vadakalais, who trace their philosophical origins to the insightful Vedanta Desika, asseverate primacy to Sanskrit and Vedas, and believe that human effort is a contributory factor to liberation, as is Divine grace. Despite these differences, however, both traditions uniformly revere the same teachers from the Alvars down to Ramanuja and largely agree in their core philosophies. The differences seen today stem primarily from social conflicts stemming from rivalries at large temples dating from the 18th century Vadakalai Iyengars follow Ramanuja and Thooppul Vedanta Desika. While Thenkalai Iyengars follow Ramanuja and Manavala Mamuni.
The main points of dissension between Vadagalai and Thengalai Iyengars are as follows:
1. Whether Lakshmi, the consort of Vishnu, is (Vibhu) co-omnipresent and co-illimitable with Vishnu;
2. Whether Lakshmi is only the mediatrix for, or the co-bestower of moksham or final beatitude;
3. Whether there is any graduated moksham attainable by the good and blessed, according to their multifarious merits;
4. Whether prapatti, or unconditional surrender of the soul to God, should be performed once for all, or after every act of spiritual rebellion;
5. Whether it (prapatti) is open to all, or is prescribed only for those specially prepared and apprenticed;
6. Whether the indivisibly atomic human soul is entered into, and permeated or not by the omnipresent creator;
7. Whether God's mercy is exerted with or without cause;
8. Whether the same (the divine mercy) means the overlooking (dhosha darsanam) or enjoyment (dhosha bogyatvam) of the soul's delinquencies;
9. Whether works (karma) and knowledge (Jnana) are in themselves salvation giving, or only lead to faith (bhakthi) by which final emancipation is attained;
10. Whether the good of other (unregenerate) castes should be tolerated according^ to their j^raduated social statuses, or should be venerated without reference to caste

                                                                                                                           
This is where the Monkey Analogy (Markata Nyaya School of Vadakalai) comes. The baby monkey clings on to the underbelly or the back of the mother monkey for transportation. That act of the baby monkey is the active effort it puts in for its transportation, security and nursing on the mother.

Human effort is necessary for grace to descend on the individual. They demand some work on the part of the individual. One has to observe Prapatti to obtain Moksa; that is self-effort on the part of the devotee. If God were to confer Moksa without rituals, prayer and Prapatti, He could be accused of arbitrariness. One has to do Sadhana (Spiritual discipline as means to attain God or realize Brahman).

Tenkalai is of the belief that God confers unconditioned Krupa (கிருபை--Krupai- Grace) to the individual without a need for ritualistic and conditioned behavior in Prapatti.

This is where the Cat Analogy (Marjara Nyaya School of Tenkalai) comes. The kitten does not have to cling on to the mother cat. The mother cat picks up the kitten by the nape of the neck and carries it. God carries the individual to Moksa without the latter’s effort. God's Grace is causeless (Nirhetuka Krpa) and so there is no need to observe Prapatti in its six-fold form

The Iyengar community traces its philosophical origins to Natamuni the first sri vasinava acharya who lived around 900 CE. He is traditionally believed to have collected the 4,000 works of all Alwars  and he  also  introduced the devotional hymns of the alvars into worship, thus mixing their Tamil veda  with the traditional Vedas written in Sanskrit. A scriptural equivalence was accepted by the community that formed in acceptance of his works, with the Sanskrit texts considered to be metaphysical  truth and the Tamil oral  variants to be based on human experience of the same This community became immersed in the dual-language worship in temples where issues of  caste were of no concern. A century or so later, Ramanuja became the principal among religious leaders who formalised the efforts of Nathamuni as a theology  Ramanuja developed the philosophy of Visishtadvaita and has been described as "the founding interpreter of [Sri Vaisnavite] scripture." While Anne Overzee says that he was a collator and interpreter rather than an original thinker, although showing originality in his method of synthesising the Tamil and Sanskrit sources,.  Amny  historians  has said that the two sets of sources "continued to be parallel to each other and not incorporative" at this time

Nathamuni and Ramanuja were both Brahmins, while Nammalvar was of the   vellala caste which their community considered to be the lowest  varna known as Shudra All three men were.Tamilinas  although Ramanuja documented his thoughts in Sanskrit as well

Among the Iyengers later  on  two sub-sects of Brahmins arose in Tamil Nadu called Vadagalai and Tengalai Ayyangars. As the words suggest the Vadagalai are supposed to be from Northern part  and tengali  from  southern  part .

Forget  about  difference  but  let  us  understand  the  siginifcance  of  U  and  Y

U  type  mark   namam  worn  by  Vadagalai  is  nothing  but  the  lower side  of  Lord Krishna s feet and  the  red  mark  signifies  Godess  Lakshmi .  where  as in  tengali  Y  signifies  both  the  feet  .